Prescot, Lancashire born outside left Harry Singleton began his senior football career at Lancashire League Stockport County in 1899 and made his Football League debut, and only League appearance for The Hatters, in a heavy home defeat to New Brighton Tower in September 1900 soon after their election to the Second Division. Joining Bury, he spent much of the remainder of 1900-01 at Gigg Lane without making their first eleven, before he was signed by First Division Everton in February 1902. He made three appearances for The Toffees in their 1901-02 campaign run but Everton failed to score in any of them as they finished runners up in the League Championship, but at the end of the season he moved on again, this time joining First Division club Grimsby Town.
He scored twice in 20 appearances for The Mariners but they were relegated at the end of the 1902-03 season, and Singleton joined Southern League New Brompton (now Gillingham) in May 1903, spending a single season at Priestfield before a move to Queen’s Park Rangers the following summer. After a single season at Loftus Road he joined newly elected Second Division club Leeds City in June 1905, where he made his debut in Tbe Peacocks’ inaugural League fixture in a 1-0 defeat at Bradford City on 2nd September 1905. His goal at Leicester Fosse on September 16th gave Leeds their first victory in their fourth League match.
He only missed one game in the entire season and of the men who started City’s first game, Singleton had the longest run in the side before missing a match, appearing in every fixture until 16th April, the 42nd contest of the campaign. He had been injured two days earlier against Stockport. According to the Yorkshire Post, Singleton was haring in on goal and had “cleared both the Stockport backs, and then had only the County custodian to face. The latter left his position to meet the attack, and brought Singleton down in a very questionable manner.”
The next season Singleton continued as first choice at the start of the 1906-07 campaign and he held his position until an injury against Burnley on 27th October when centre forward David Wilson tragically lost his life. The Yorkshire Post wrote: “If only Singleton had had a little more resolution when facing the backs, there would have been nothing at all to criticise. He took and gave his passes splendidly, but there was often wanting just that shade of devil which makes the last breach in the enemy’s line.” After that match he played only once more in City colours in January 1907. Flaneur wrote in the Leeds Mercury of his appearance in a “thrilling victory over West Bromwich Albion” on 5th January, “Singleton, who played for the first time since his injury in the fatal match against Burnley in October, was more effective than I have previously seen him, and his centres were always executed with great judgement.” Having scored 7 times in 51 appearances for Leeds, he joined newly founded Huddersfield Town at the end of the campaign, but had retired by the time they joined The Football League three years later.