In 1906 Hilsdon was recommended to then-Chelsea manager John Robertson, who had been advised that Hilsdon would be available for transfer; so enthralled was Robertson with Hilsdon's ability that he promised to turn him into Chelsea's next center forward. Hilsdon joined Chelsea later that year on £4 a week wages. He scored five goals on his debut in a 9-2 win over Glossop North End, and would later score six in an FA Cup tie with Worksop Town, a club record which remains unequaled. The club program described him as “living proof that to become a first-class footballer it is not necessary to be born north of the Tweed”.
Hilsdon scored 27 goals that season, which helped earn Chelsea promotion to the First Division in their second year of professional football. Within three years he had notched 76 goals in 99 appearances. His later days with Chelsea were hindered by problems with injuries and his personal life, including a battle with alcoholism, though he did score 19 goals in 1910-11. He became the first Chelsea player to score 100 goals, and ended his time there with 108 from 164 games. He is currently the club's 9th highest goal scorer of all time.
Hilsdon received international recognition for England, often playing alongside his Chelsea team mate, Jimmy Windridge. Shortly after joining Chelsea he was selected to play for a Football League XI, for whom he hit a hat-trick in a 6-0 win over the Irish League on his debut. He made his England debut in February 1907 against Ireland. He scored four goals for England in a 7-0 win over Hungary and two apiece in wins over Ireland, Austria, Wales and Bohemia. In all, he managed to score 14 times in just eight international games for England, eight of his goals coming from games in England's first overseas tour in 1908.
In 1912 he returned to West Ham, and was top scorer for them in the 1912-13 season, scoring 17 goals in 36 games. He was known at this point as the "old international", even though he was still only 27 years of age. Hilsdon played for West Ham until 1915, and during his two spells there he recorded 92 Southern League appearances, and scored 35 goals. Hilsdon also played in four World War I games for the east London outfit. He is also credited with helping the development of young West Ham striker Syd Puddefoot.
During the war Hilsdon tried to avoid active service and was caught by the police hiding in a chicken run, and was called up. This affected him greatly, and in the words of his son, he “copped the mustard gas at Arras.”
After the War, he worked as a teaboy on building sites, ran a pub and organised raffles in East End pubs.
He died in Leicester in 1941 and only four people came to the funeral. There is no stone to mark Hilsdon's grave. A weather vane modelled on Hilsdon is still a feature of Stamford Bridge, Chelsea's home ground.