Rotherham born full back Len Smelt started with junior clubs Kimberworth Wesleyans in 1906 and Rotherham Main Institute in 1907 before joining Rotherham County later that year, moving to Second Division Gainsborough Trinity in August 1908, for whom he made his Football League debut against Birmingham that September, scoring in his next game in a 2-1 win at Grimsby Town, and notching twice that season in 8 appearances, his only career goals.
He joined non league Sutton Junction at the end of the 1908-09 season, playing for Masbrough Thursday in 1911 before re-joining Rotherham County, staying 2 years before moving to Chesterfield Town in 1913. After the First World War he joined First Division Burnley in May 1919 and missed only 4 matches in their first 4 post war seasons, which saw them finish runners up in the League to West Bromwich Albion in 1919-20 before going one better, finishing as League Champions in 1920-21. He was also a member of the Burnley team which contested the 1921 Charity Shield losing to Tottenham Hotspur. In 1921-22 they finished third to Liverpool.
In 1924 he was part of their FA Cup semi final team losing 3-0 to Aston Villa at Bramall Lane. Smelt’s final game for the Clarets on 18th April 1925 at the age of 41 years and 132 days, and after 248 appearances he joined Barrow in June 1926, playing a single season and 39 matches for The Cumbrians before joining non league Frickley Colliery in 1927, also subsequently playing for Hurst in 1928.