Reading, 2012–15 Kirby joined her hometown club
Reading at the age of seven and worked her way through the youth teams. She made her debut for the first team at the age of 16 but quit football the following year after an onset of depression, brought about by the death of her mother. Kirby returned to the club in 2012 and went on to become the
FA Women's Premier League Southern Division's top scorer for the
2012–13 season, with 32 goals in 21 appearances. With Reading promoted to the newly formed
Women's Super League 2 for 2014, Kirby helped the team achieve third place with 24 goals in 16 appearances. She ended the season as the league's top goalscorer; netting four against
London Bees, as well as
hat-tricks against
Durham,
Watford and
Doncaster Rovers Belles. Shortly after, she became the first female player to receive a professional contract from the club. At the 2014 FA Women's Awards, Kirby was named the inaugural WSL2 Players' Player of the Year. Kirby continued her goalscoring form into the
2015 WSL2 season, taking 11 goals in five league appearances for Reading, including all four goals in a 4–2 away win against
Yeovil Town and five goals in a 7–0 win against London Bees. Following the
2015 FIFA Women's World Cup, Reading accepted an undisclosed transfer fee from Chelsea and she completed a move in July 2015. It was reported that the fee of between £40,000 and £60,000 constituted a British record, although Chelsea denied this was the case and Kirby was not aware of the figure.
Chelsea, 2015–24 At the
2015 FA Women's Cup Final, staged at
Wembley Stadium for the first time, Kirby was a
cup-tied spectator for Chelsea's 1–0 win over
Notts County. It was Chelsea's first major trophy. In October 2015, she scored twice in Chelsea's 4–0 win over
Sunderland which secured the club's first
FA WSL title; a league and cup
double. The same month, Kirby scored Chelsea's first ever
UEFA Women's Champions League goal in a 1–0 win over
Glasgow City. match, November 2019 Kirby's form extended into the
2016 FA WSL season. In April, she secured Chelsea's return to Wembley Stadium by scoring a late,
extra-time winner against
Manchester City in the FA Women's Cup semi-final. Four days later, she scored both goals in Chelsea's 2–0 WSL win at
Arsenal. On 22 April 2018, Kirby was awarded the
PFA Women's Players' Player of the Year and the
Football Writers' Women's Footballer of the Year for the
2017–18 season. In February 2020, Chelsea announced that Kirby was diagnosed with
pericarditis, which had ruled her out of the team since November 2019. She overcame her infection, despite being told by cardiologists that she may never play again, and played 70 minutes in Chelsea's
FA Community Shield win against Manchester City on 29 August 2020. On 9 December 2020, Kirby's 2 goals in a 5–0 win against
Benfica in the
UEFA Women's Champions League, saw her overtake Eniola Aluko as Chelsea's all-time goal scorer, with her 69th and 70th goals for the club, five years after signing. During a match against her former club, Reading on 10 January 2021, Kirby scored four goals lifting Chelsea to a 5–0 win. In the 2021
FA Women's League Cup final match against
Bristol City W.F.C., Kirby scored two goals and created four assists as defending champions Chelsea won 6–0 at Vicarage Road. Kirby was singled out by observers as the top performer for Chelsea during their double-winning 2020–21 campaign. She later won
FWA's 2021 ''Women's Footballer of the Year'' award. On 5 December, Kirby scored the opening goal in the delayed
2020–21 FA Cup final against Arsenal, helping her team lift the trophy and secure the domestic
quadruple of the 2020–21 season, the first English women's club to achieve the feat. In the
2023–24 League Cup quarterfinal, Kirby scored two goals and made two assists in the 5–0 win against
Sunderland. On 4 May 2024, it was announced that Kirby would leave Chelsea at the end of the 2023–24 season. On 22 February 2026, she scored and provided an assist in Brighton's 2–1 win over
West Ham United, helping her team to reach the quarterfinals of the
FA Cup in a performance described as having "rolled back the years". ==International career==