McMahon was an orthodox left-arm spin bowler with much variation in speed and flight who was spotted by Surrey playing in club cricket in North London and brought on to the county's staff for the 1947 season at the age of 29.

[6] The emergence of Tony Lock as a slow left-arm bowler in 1949 brought a stuttering end of McMahon's Surrey career.

[6] In 1953, Lock split the first finger of his left hand, and played in only 11 of Surrey's County Championship matches; McMahon played as his deputy in 14 Championship matches, though a measure of their comparative merits was that Lock's 11 games produced 67 wickets at 12.38 runs apiece, while McMahon's 14 games brought him 45 wickets at the, for him, low average of 21.53.

Somerset's slow bowling in 1954 was in the hands of leg-spinner Johnny Lawrence, with support from the off-spin of Jim Hilton while promising off-spinner Brian Langford was on national service.

Though he played some games for the second eleven later in August, he regained his place in the first team for only a single end-of-season friendly match, and he was told that his services were not required for the future, a decision, said Wisden, that "proved highly controversial".

The obituary recounts a further escapade in second eleven match at Midsomer Norton where a curfew imposed on the team was circumvented by "a POW-type loop" organised by McMahon, "with his team-mates escaping through a ground-storey window and then presenting themselves again".

[16] As the only Somerset second eleven match that McMahon played in at Midsomer Norton was right at the end of the 1957 season, this may have been the final straw.