Hannover 96 Mertesacker joined the youth system of
Hannover 96 where he played under his father Stefan, one of the youth coaches, until age 15. While juggling his football commitments and training, he completed his '
Abitur' at Carl-Friedrich-Gauß-Schule, a
comprehensive school located in nearby
Hemmingen noted for its sports program, and subsequently carried out his '
Zivildienst' at a centre for handicapped people in Hanover. He was promoted to the first team for the
2003–04 season and made his league debut in November 2003, starting against
Cologne in the unfamiliar role of right-back. At the time of his debut he was the youngest German-born player in the
Bundesliga. Mertesacker was not seen as an exceptional player at that time and had thought about changing sports. He returned to the first team during the latter half of the season and contributed to Hannover 96's successful battle against relegation. The following season began more auspiciously as he scored his first goal as professional, a last-minute equaliser against
Borussia Dortmund in August 2004. Having established himself as first-choice centre back, his strong performances and clean disciplinary record did not go unnoticed by new national team coach
Jürgen Klinsmann, who called him up and eventually handed him his senior international debut in October 2004. In October 2018, Mertesacker returned to Hanover for his charity-cum-
testimonial match, which featured his former teammates from Hannover 96 facing off against a "World XI" team composed of his former teammates from Arsenal, Werder Bremen and the Germany national team. Instead of holding his testimonial match in London, where he was based when he retired, he chose Hanover as it was where his career began.
Werder Bremen In August 2006, Mertesacker moved to
Werder Bremen in a €5 million transfer deal after a highly impressive performance in the
2006 World Cup, in which Germany finished third. At the time of his transfer, he and Brazilian midfielder
Diego, who joined from
Porto, were jointly Bremen's most expensive signings in the club's history. Despite missing the first month and a half through an injury sustained at the World Cup, he quickly made the centre-back position his own upon his return to the starting eleven. In November, he scored his debut Champions League goal in a 1–0 win over
Chelsea to end the
Premier League winners' unbeaten streak in the season's competition. Upon his first return to the
AWD-Arena for the first game of the second half of the season, he refused to celebrate after scoring against his boyhood club. The
2007–08 season was a mixed bag for Mertesacker. He started in nearly all of Bremen's league and European fixtures and received his first red card in his professional career in a 6–3 loss against
VfB Stuttgart. Bremen finished runners-up in the league winning only two games fewer than champions
Bayern Munich and managed to seal a place in the next season's
Champions League. At the end of the season, he signed a two-year extension to his original contract. After returning from the
Euro 2008, Mertesacker again missed the beginning of the new season with a knee injury and through illness. In September, he returned to the starting line-up. He scored the opening goal in the
DFB-Pokal semi-final away at northern rivals
Hamburger SV to break the deadlock after a goalless first half, but the home side equalised, forcing the match into extra time and Bremen eventually triumphed 4–2 on penalties. He was ever present for the rest of the season until injury forced him off in the
UEFA Cup semifinal second leg against Bundesliga rivals Hamburg. It was later revealed that he had torn ligaments in his right ankle and required surgery. He was ruled out for the rest of the season, as well as the
UEFA Cup final loss against
Shakhtar Donetsk and
DFB-Pokal final, which they won. He scored four goals in all competitions, including a crucial equalizer against
VfL Wolfsburg. Mertesacker began the
2009–10 season well with a 5–0 win over
FC Union Berlin in the
2009–10 DFB-Pokal, the first game of the season. In October, he scored his first goal of the season in a 2–0 win against
1899 Hoffenheim and a last-minute equalizer in the clash against table-toppers Bayer Leverkusen in February. He played 33 Bundesliga matches in total, scoring five goals in the process. In the
2010–11 season, Mertesacker made 30 Bundesliga appearances, scoring two goals. He averaged 46.3 passes per game, the third-highest in the Bremen squad, and the second highest pass success rate, with 82%, demonstrating another facet of his game. Over the course of his final two seasons at Bremen, Mertesacker received just one yellow card in 63 league matches. He averaged less than one foul per game, cementing his reputation as an astute reader of the game, defying critics' predictions that his height would render him clumsy and having a tendency to frequently concede fouls. In February, Mertesacker suffered an ankle injury in the win over Sunderland away at the
Stadium of Light and faced a long-term spell on the sidelines. Prior to his injury, he featured in the draw at
Bolton Wanderers and the 7–1 victory over
Blackburn Rovers at
Emirates Stadium. "Unfortunately he has had surgery and we have lost him for a while," said Arsène Wenger. "How long, I don't know. He had reconstruction of his ligaments. So it will be long term." He had not featured for Arsenal for the remainder of the season. In his second season, Mertesacker played in Arsenal's first two matches, helping the team keep clean sheets against Sunderland and Stoke. "I think we have a better situation than last year," he said. "The team is full of characters, good players and every position [has competition]." He featured four times in September, forging a fine partnership with
Thomas Vermaelen (who replaced Koscielny due to injury) in the process. The German centre back was named man of the match after an excellent performance in a 1–1 draw with
Manchester City at the
Etihad Stadium. against
Sunderland in 2012 In October, Mertesacker continued to perform well, making four appearances and helping the club to victories over
Norwich City and
Queens Park Rangers. Laurent Koscielny praised the German's performances, saying, "I am happy for Per because he's a nice guy, very important in the dressing room. He's a joker so he's good for the team. I'm happy because he's played well this season and it's good for the team." Mertesacker was an ever-present throughout November. He scored his first goal for the club in the 5–2 win over
Tottenham Hotspur and was voted man of the match for his performance in the 0–0 draw with
Aston Villa. "It was amazing from the very start," he told Arsenal after the Tottenham game. "It was very good to score because we were one man up and they were dropping off. I kept standing in the box and tried to be lucky. The ball from
Theo [Walcott] was very good and it was a good day to score." Mertesacker made five appearances in December, missing only the trip to
Olympiacos in the
Champions League and the home win over
Newcastle United. On being drawn against Bayern Munich in the
Champions League round of 16, he said, "We will face a good team in Germany. They are top of their league and went through to the knockout stage in a phenomenal way. They only conceded seven goals in the first half of the season. [But] they have a little break now and can rest a bit. Maybe it's a good opportunity for us to face them in February because we will be in our rhythm. We will hopefully go through the Christmas period in a strong way. We can do that." Mertesacker captained Arsenal for the first time in the
FA Cup win over
Brighton & Hove Albion in January, and appeared in every game save for the draw at
Southampton on New Year's Day. "We are always looking to win something and we can achieve something with this group," he told Arsenal. "We have a lively group so our thoughts are now on the next match. That's the most important thing for us, not what's going to happen in May. We have a few targets in our team that are possible this year. We won't talk about it, we'll just see what happens in the next few important weeks on the pitch." Mertesacker started four games in February, missing only the FA Cup loss to Blackburn at the Emirates. "It's always special to face a German team," the defender said ahead of the Champions League tie against Bayern. "[Me and
Lukas Podolski] are looking forward to it because Bayern are a great team and are so consistent this year. It's a special game for German players to play against a team from their home country." in the
Premier League Mertesacker was a mainstay in March, playing every single minute of Arsenal's four games. The centre back was on target in the defeat at Tottenham and was a key component in the defence that kept clean sheets against both Bayern Munich and
Swansea City. "It rained cats and dogs, especially in the second half," he said after the win in south Wales, in
Swansea. "It was very slippery but it was a vital win." In April, Mertesacker was shown a red card at
West Bromwich Albion in the first game of the month. The defender returned to the team after suspension and was named man of the match against
Fulham after scoring the only goal away at
Craven Cottage. "I think they've been terrific – not only defending very well but also creating goals for us at the other end like they did last week against Fulham," said goalkeeper
Wojciech Szczęsny on the partnership between Mertesacker and Koscielny. "They're getting the credit they deserve because they work very hard and they're very honest lads. I'm very happy for them and it's much easier to play behind them when they are in that kind of form." Mertesacker impressed at the back alongside Koscielny in May. The German defender was given the captain's armband in Arsenal's last game of the season when
Mikel Arteta went off injured. "I think it is good for us to play against teams who are under pressure," he said after the win against Queens Park Rangers [who were on the brink of relegation]. "It helps us keep our focus on a high level." Mertesacker was named as the temporary
captain of the side after injuries to Thomas Vermaelen and Mikel Arteta at the beginning of the 2013–14 season. He scored his first goal of the season against Stoke following a free-kick from compatriot
Mesut Özil. After his
man of the match performance away to
Borussia Dortmund in the
Champions League helped Arsenal to a 1–0 win, Mertesacker's influence was cited as a significant factor in Arsenal's excellent start to the
2013–14 season, which saw the team leading the
Premier League at the end of November. As Mertesacker's great run continued, he was voted as a part of the Premier League Team of the Year, along with teammate
Aaron Ramsey. On 13 January 2014, Mertesacker made his 100th official appearance for the
Gunners in a 1–2 away win over Aston Villa. On 4 March 2014, Mertesacker signed a new contract with Arsenal. On 12 April 2014, Mertesacker scored an 82nd-minute equalising goal for Arsenal in the
FA Cup semi-final against
Wigan Athletic. The match finished 1–1 after
extra time, with Arsenal winning 4–2 in a
penalty shootout. He had earlier conceded the penalty that had put Wigan 1–0 up. On 17 May 2014, Mertesacker started in the
2014 FA Cup Final as Arsenal beat
Hull City 3–2 at
Wembley Stadium. After initially featuring sparingly due to injuries in the 2014–15, he returned to captain Arsenal in the
2015 FA Cup Final at
Wembley in a 4–0 victory over Aston Villa. He scoring the third goal, a header, during the second half. After healing from injury, Mertesacker remained a mainstay in the Arsenal backline, playing alongside Laurent Koscielny. With Arsenal making a charge towards the title, Arsène Wenger singled out Mertesacker for praise, calling him an "important leader in the dressing room and a respected one". On 24 January 2016, in a match against
London rivals Chelsea, Mertesacker was sent off after 18 minutes for a late tackle on
Diego Costa, who later scored the only goal of the game at Emirates. However, he sustained an injury against
Lens in the 2016–17 pre-season, undergoing knee surgery in his native Germany later that month. Following a clash between Arsenal and
Viking,
Arsène Wenger confirmed that Mertesacker would be absent until December. Despite the injury he was named club captain following the retirement of Mikel Arteta. He was a second-half substitute on the last day against Everton. On 27 May 2017, Mertesacker made his only start of the season, in the FA Cup final against
Chelsea, which Arsenal won 2–1. He made a number of important tackles during the match and his performance was praised by opposition manager
Antonio Conte, who stated that Mertesacker was a "perfect example for any young professional football player," adding that "what he did today was just a consequence of an unbelievable attitude every day." Arsenal later confirmed the 2017–18 season would be Mertesacker's last, before becoming the head of the club's academy the following year. On 7 January 2018, Per Mertesacker captained the Arsenal team in an FA Cup game away against Nottingham Forest and scored a goal to make the score 1–1, with the game eventually finishing 4–2 to Forest, before featuring in his last ever game for the club in a win against
Burnley on 6 May 2018. ==International career==