Billy Clifford Gilmour was born on 11th June 2001 at Ayrshire Central Hospital in Irvine to Billy and Carrie Gilmour. He lived in Ardrossan. His father served in the Royal Navy and played junior football for Ardrossan Winton Rovers.
Billy went to Stanley Primary School in Ardrossan and played developmental football at Tass Thistle in the Three Towns before heading to Grange Academy in Kilmarnock as part of the Scottish Football Association’s Performance School Programme. The SFA set up the Performance Schools programme in 2012 where they enrolled the best under 12 players from around the country.
At aged 15 he was invited to train with Ranger’s first team making his debut for the Under 20 development team in 2016. Despite holding talks with Billy’s family to persuade him to stay with Rangers, Billy chose to join Chelsea in July 2017, aged only 16, joining their Under 18 squad. Gilmour chose Chelsea because “at Rangers, I just needed to be the best in my group to come through. At Chelsea, I’ve got to be one of the best in the world”.
After he turned 17, Billy signed his first professional contract with them and made his debut on 10th July 2019 in a pre-season friendly against Bohemians in Dublin.
He made his Premier League debut on 31st August against Sheffield United coming on in the 84th minute. He played his first full match against Grimsby Town on 25th September.
On 29th May 2021 Billy was part of the Chelsea team that won the UEFA Champions League, beating Manchester City 1-0, lifting the trophy like another North Ayrshire man before him in 1967, Bobby Lennox of the Lisbon Lions.
Billy has represented Scotland at Under 16, Under 17 and Under 21 levels. Then, in May 2021, Steve Clarke included Billy Gilmour in the Scotland Euro 2020 squad, making his first appearance on 2nd June in a friendly against the Netherlands. On 18th June he made his first start debut in that 0-0 draw against England and was awarded Man of the Match.
In 2022 Billy transferred to Premier League club Brighton and Hove Albion and then in August 2024 to Italian team SCC Napoli.
He remained in the Scotland squad for 2022 World Cup qualifiers and was named in the squad for the UEFA Euro 2024 finals in Germany.
Billy gained his 40th cap for Scotland on 9th June 2025, when Scotland beat Liechtenstein 4-0.