He joined the Parkhead club at eighteen in 1917 and went straight into the first team, at outside-left, although he had arrived as a centre-forward and played in a number of positions up front. And he stayed there for a decade, over four hundred starts at a goal at well under every three games, four League titles, three Scottish Cups that might have been four had he not been injured for the 1926 final, won by St. Mirren. And to that he added four caps, which would probably have been many more but for the inestimable Rangers left-winger, Alan Morton. And amidst all the footballing success McLean had in 1920 married young. He had been twenty-one, recorded as a Rivetter, as his father also was, his bride, Elizabeth McConnochie, just twenty, from Ayrshire. They were wed in Patna, settled in Partick and over the next decade and a half were said to have three sons, the last born in 1934 by when Adam was turning out for a final season at Partick Thistle, the road to which had taken in Sunderland and Aberdeen. In 1928 as he turned thirty he had a dispute with Celtic that was not resolved. It had led him to move on for two good seasons on Wearside. That was before a return north to the Granite City, where the goals to games was maintained for an additional three seasons, only ended when McLean exposed gambling on games by team-mates and with the cooperation of the club moved on, ostensibly following an application by him to manage Linfield back in Belfast but actually to Glasgow and Partick.

On finally hanging up his boots in 1934 Adam turned to coaching, for example in 1936 at Brann Bergen in Norway, and scouting, for Huddersfield, before in 1938 being appointed assistant trainer back at Firhill. And there he remained there until retirement in 1962, including a brief period as care-taker manager in 1959. In fact he was still to live close to its ground from re-joining The Jags until his death in 1973 at the age of seventy-five, recorded as a Retired Football Trainer, and survived by Elizabeth by just three years.