In 1945 he was appointed as manager of Port Vale, before he returned to Coventry as manager in 1947. His time at both clubs was unsuccessful, and he spent the next decade in non-league football as manager of Stafford Rangers and Rugby Town. He returned to Coventry as manager in 1957 and led the club to promotion out of the Fourth Division in 1958–59, but was sacked in 1961. His last management post was at Chelmsford City between 1963 and 1965, he led the club to second in the Southern League in 1963–64.
Frith was appointed manager of Port Vale in August 1945. The 1945–46 season was uneventful and he seemed to settle into management quite well. In preparation for the first season of post-war football, he signed experienced forward Colin Lyman from Tottenham Hotspur for 'fairly substantial fee', full-back Garth Butler from Derby County, and half-back Norman Hallam from Chelsea. He sold goalkeeper Arthur Jepson to Stoke City for £3,750. However after a poor start to the season, he resigned in October 1946 over a policy difference with the club's directors. He claimed the board refused to back his suggestions for new payers, interfered in team selection and failed to grant him a three-year contract – claims which the club denied. The "Valiants" went on to finish the 1946–47 campaign in tenth place in the Third Division South under Gordon Hodgson.
After leaving Port Vale, Frith returned to Highfield Road as assistant to Dick Bayliss, and also played seven league games. Following Bayliss' death, Frith was appointed as manager of Coventry City in August 1947, remaining in that position until November 1948. Coventry finished the 1947–48Second Division season in tenth place, and went on to end the 1948–49 season just two points above the relegation zone under Harry Storer's stewardship.
His side flirted with the prospect of a second successive promotion in 1959–60, but ultimately finished in fifth place. They failed to push for promotion in 1960–61, and ended the campaign in fifteenth place. On what was known as 'Black Saturday', 25 November 1961, Coventry were dumped out of the FA Cup by non-league King's Lynn, and Frith was sacked by chairman Derrick Robins. He was replaced by Jimmy Hill, who took Coventry to a fourteenth-place finish in 1961–62. He later managed Chelmsford City, and led the "Clarets" to second and fifth-place finishes in the Southern League in 1963–64 and 1964–65.