Billy Clifford Gilmour is a Scottish professional footballer who plays as a midfielder for Premier League club Chelsea, and the Scotland national team.Gilmour developed his career as part of Rangers Academy. His progress saw him fast-tracked towards the first team, making his debut for the under-20 development team in December 2016 at the age of 15 and being invited to train with the first team squad the following month by manager Mark Warburton. Gilmour was given a squad number and, following Warburton's departure from the club, was twice included in the provisional squad for Scottish Cup matches by Rangers caretaker manager Graeme Murty.
Rangers, however, announced in May 2017 that they had reached an agreement for Gilmour to join Chelsea for a "significant fee".Reports suggested that Chelsea would pay an initial development fee of around £500,000, with potential further payments dependent on his progress.Gilmour became officially contracted to Chelsea in July 2017, following his 16th birthday. He joined the club's under-18 squad, making a goalscoring debut in an Under-18 Premier League match against Arsenal during September 2017, and going on to score in each of his first three appearances. In July 2018, after turning 17, Gilmour signed his first professional contract with Chelsea. He made his Premier League debut on 31 August against Sheffield United, coming on in the 84th minute for Tammy Abraham. He made his full debut on 25 September, playing the full 90 minutes in a 7–1 EFL Cup win against Grimsby Town. Gilmour was added to the Chelsea first-team squad on a permanent basis in February 2020. He was widely praised for his performance in a 2–0 win against Liverpool in an FA Cup tie on 3 March. Gilmour later made his first Premier League start later that week on 8 March against Everton, earning Man of the Match honours in a 4-0 win. In July 2021, Gilmour joined fellow Premier League club Norwich City on a season-long loan. He played 28 times for Norwich during the 2021–22 season, but the team finished last in the 2021–22 Premier League and were relegated.
In June 2022, Chelsea exercised an option to extend Gilmour's contract to the end of the 2023–24 season.