Henderson started out in the PDC circuit and played one tournament in Scotland as well as the
2003 UK Open where he lost in the first round, having won his preliminary match. He then qualified for the
2005 BDO World Darts Championship, where he beat
Stephen Bunting in the first round before losing in round two to
Martin Adams – hitting a record thirteen 180s (for a five-set match) in the 3–2 defeat. Henderson then reached the quarter-finals of the 2005 British Open and the last 32 of the 2005
Winmau World Masters. Henderson reached the final of the 2007 British Open. He beat
Tony O'Shea in the quarter-finals and
Ted Hankey in the semis before losing to
Gary Anderson in the final. This was followed however with failure to qualify for the
2008 BDO World Championship and an early exit from the 2007 World Masters.
2008–2009 2008 was a good year for Henderson, reaching the semi-finals of the Norway Open and the quarter-finals of the WDF Europe Cup. On 20 September 2008 Henderson captured his very first title, winning the 2008 British Open. He scored notable wins over Edwin Max and
Dave Chisnall to earn a spot into the televised stages which were shown live on
Setanta Sports. He then defeated
Gary Robson in the quarter-finals and
Mareno Michels in the semis before avenging his defeat over Anderson twelve months previously by beating him in the final to win the £3,000 top prize. The win also helped Henderson finish fourth in the BDO International Grand Prix, earning him another £2,750 for his efforts. He also shot up the world rankings as a result of the win, moving him into the WDF's top 20. He then captured the German Open in 2009, beating
Stephen Bunting in the final which elevated Henderson to seven in the WDF rankings.
2010–2011 Henderson then qualified for the
2010 BDO World Championship, winning one of four places available from the Inter-Playoff Qualifiers in
Bridlington. He was defeated in the second round by
Scott Waites. Henderson failed to qualify for the 2011 tournament, but did qualify for the
2010 Grand Slam of Darts where he finished third in his group. After being defeated by Mervyn King he was accused of standing in front of the oche, however after watching the match again, King admitted that he had over-reacted and apologised to Henderson in a pre-match interview. On 15 January 2011, Henderson came through qualifying at the PDC Q-School event and has therefore left the British Darts Organisation. On joining the PDC he said "It means everything to me the first two days were hard and I felt a lot of pressure today but to qualify, so I'm delighted I did it." In the 2011 Derby championships, Henderson hit a
nine-darter in his second leg of the second round beating Andy Hamilton 6–5 and earning £800. Henderson qualified for the
2011 World Matchplay where he beat
Colin Lloyd 10–7 in the first round, before losing to
Andy Hamilton 13–11 in the second round. He defeated on form
Justin Pipe 2–0 at the
World Grand Prix 2011, he went on to reach the quarter finals losing to eventual runner up
Brendan Dolan 4–1.
2012–2020 Henderson reached his first
PDC World Championship in
2012, but was beaten by three-time World Champion,
John Part, 0–3. He only managed to win 2 legs during the match, with Part stating afterwards that "John struggled and wasn't himself". His best result on the
2012 Pro Tour was in reaching the quarter-finals of the 16th Players Championship event, where he lost to Nick Fullwell 2–6. Henderson was beaten in the last 16 of the
Qualifier for the
2013 World Championship. He was ranked world number 39 after the World Championship. Henderson qualified for the
2013 UK Open by finishing 50th on the Order of Merit to enter the event in the second round. He enjoyed his best ever run in the tournament by beating Dave Place,
Scott Rand and
Kevin McDine to advance to the last 16. He played
James Wade and lost 9–4. Henderson reached the quarter-finals of a
Players Championship played in
Killarney for the second consecutive year as he beat
Mark Webster,
Ian White and
Justin Pipe before being whitewashed 6–0 by
Darren Webster. He qualified for the
2014 World Championship through the
ProTour Order of Merit having claimed the ninth of sixteen places that were available to non-qualified players. Henderson started his first round match brightly as he took a 2–0 lead against seventh seed
Dave Chisnall which included a 132 finish of bull, bull, double 16. He threw for the match in the third set but lost the leg and the set as Chisnall fought back to level the game. Henderson survived four match darts from Chisnall in the final set as he pulled off a big shock win in a performance he rated as the best of his career. Another tight match followed against
Mark Webster with Henderson missing three darts at tops to seal a 4–2 win, and then went on to lose the deciding set to bow out of the tournament 4–3. At the
2014 UK Open, Henderson was beaten 5–1 by
Jelle Klaasen in the second round. He beat
Steve Hine 6–4,
Peter Wright 6–5 and
Simon Whitlock 6–2 (with an average of 106.12) to reach the quarter-finals of the
German Darts Masters, where he lost 6–2 against
Adrian Lewis. In the rest of the year he lost in the last 16 of two
Players Championships and qualified for three European Tour events, losing in the second round in two and the opening round of the other. The opening four sets in Henderson's first round
2015 World Championship match against
Vincent van der Voort went with throw to send it into a deciding set. Van der Voort hit a crucial 157 finish with Henderson waiting on 80 for the match and from there the Dutchman won back-to-back 14 dart legs to knock him out. A pair of last 16 finishes helped Henderson enter the
UK Open at the third round stage and he eliminated Steve Douglas 9–7 and then retained his composure when
Daryl Gurney won five legs in a row to lead 8–7 by beating him 9–8. This matched Henderson's best ever run the event, but it came to a sudden end when he lost 9–2 against
Peter Wright. At the
German Darts Masters, Henderson defeated
Michael Smith 6–4 and then averaged 102.48 in a 6–0 whitewash over
Andrew Gilding. He improved upon that in the quarter-finals by averaging 107.72 during a 6–1 victory against
Brendan Dolan and knocked out
Adrian Lewis 6–4 to reach his first PDC final. Henderson played world number one
Michael van Gerwen and he sent the match into a final leg decider, after being 3–0 down, which he lost without getting a dart for the title. He suffered first round exits at the
World Matchplay (10–2 to
Phil Taylor) and the
World Grand Prix (2–0 in sets to
Gary Anderson), but then defeated
Robert Thornton 6–4 at the
European Championship. Henderson then took advantage of a poor performance from
Rowby-John Rodriguez in the second round to thrash him 10–2 and reach his first major quarter-final in over four years, where he lost 10–4 to
Peter Wright. After taking the opening set in his first round match at the
2016 World Championship, Henderson went on to lose 3–1 against
Darren Webster. One semi-final and a quarter-final appearance in the
qualifiers helped him finish 17th on the Order of Merit for the
UK Open. Henderson saw off
Magnus Caris 9–4, before losing 9–6 to
Adrian Lewis in the fourth round. His second semi-final of the year was at the 14th
Players Championship event and he was knocked out 6–4 by
Michael van Gerwen. He was ousted 6–3 by
Gary Anderson in the first round of the
Players Championship Finals. He won the opening two sets against
Andrew Gilding in the first round of the
2017 World Championship, before it was levelled at 2–2. Henderson missed one match dart in the deciding set and it would eventually go to a sudden-death leg. Gilding won the bull to throw first and took the leg to eliminate Henderson. Following
Gary Anderson's withdrawal from the
2019 Premier League, Henderson was selected as one of nine 'contenders' to replace him. A great boost for his Red Army following of his fellow Aberdeen FC fans. He played a one-off match against No. 1 PDC-ranked
Michael van Gerwen on night five in
Aberdeen. The match resulted in a draw. Henderson returned to the Premier League in 2020 under the new tag of 'Challenger', once again in
Aberdeen. However, he was beaten by
Nathan Aspinall.
2021 Henderson, alongside
Peter Wright, won the 2021
PDC World Cup of Darts playing on behalf of Scotland. It was his first PDC Major Tournament win.
2022 Henderson failed to qualify for
2022 PDC World Darts Championship, missing this event for the first time since 2013. He continued to struggle throughout 2022, but was again nominated for the
2022 PDC World Cup of Darts, where he was defending the title alongside Peter Wright. Together they made it to the Quarterfinals, where they lost against England. At the end of the season he dropped out of top 64 of PDC Order of Merit, failing to qualify for the World Championship for a second time in a row and lost his Tour Card after the 2022 season.
2023 Henderson was unable to retain his Tour Card at UK Q-School and played on the PDC Challenge Tour. He secured two titles during the year and was battling for second place on the PDC Challenge Tour Order of Merit. After losing in an early round of the last PDC Challenge Tour event, Henderson had to hope that
Andy Boulton,
Cam Crabtree and
Owen Bates would not make the final. Boulton and Crabtree dropped out at the last sixteen. Despite facing multiple match darts against
Michael Warburton, Bates made it to the final and clinched second place, therefore Henderson did not get his Tour Card back via the Challenge Tour by just £175, finishing 3rd overall in the rankings. This result also denied Henderson the chance to qualify for the
2024 PDC World Darts Championship. Aside from competing on the Challenge Tour, Henderson later made his World Seniors Darts debut at the
2023 World Seniors Darts Matchplay in September. He was eliminated in the first round to Canadian player
David Cameron 8–4.
2024 Unable to win a Tour Card at Q-School, Henderson continued playing on the
PDC Challenge Tour in 2024. He made a final at
Challenge Tour 12, where he lost to
2012 BDO World Champion Christian Kist 6–3. Henderson also lost to eventual winners
Danny Jansen and
Noa-Lynn van Leuven in
Challenge Tour's 2 and
6 respectively. Henderson ended the Challenge Tour in 11th place on the order of merit. Henderson also accepted an invitation for the
2024 World Seniors Darts Championship. He became the World Seniors Darts champion at the first time of asking, defeated
Colin McGarry 5–0 in the final. Henderson suffered a round 1 exit at the 2024 World Seniors Darts Champion of Champions in March, after losing to
Andy Hamilton 10–8. Henderson good run of fortune returned at the
2024 World Seniors Darts Matchplay in October, beating defending champion
Leonard Gates in the final 9–6. Henderson later claimed his third Seniors title at the 2024 World Seniors Masters in November, defeating fellow Scotsman
Robert Thornton in the final in a deciding leg 6–5. Henderson performance in the 2023 Challenge Tour allowed him to qualify for the
2024 UK Open. He made it to the third round of the tournament before losing to
Gian van Veen 6–3.
2025 At the
2025 World Seniors Darts Championship, Henderson started off with a 3–2 victory over
Chris Mason, before being knocked out of the quarterfinals to Welshman Derek Coulson 3–1. Henderson also suffered another quarterfinal exit at the 2025 World Seniors Champion of Champions to former
BDO World Champion Richie Burnett 5–2. Henderson was due to start his defence of the World Seniors Matchplay in November against either
Steve Beaton or
Vincent van der Voort after their round 1 match. But the tournament never commenced, following the unexpected collapse of the WSD in August. Henderson again competed on the
PDC Challenge Tour, where he made one final in
Challenge Tour 3, but suffered a whitewash defeat to
Beau Greaves. Henderson ended the Challenge Tour 43rd on the order of merit. Henderson lost to
Graham Usher 6–3 in the first round at the
2025 UK Open. Henderson has also made competitive appearances in the MODUS Super Series.
2026 Henderson made his 4th appearance on the
PDC Challenge Tour. == Personal life ==