Shelbourne went on to mark the inaugural season with the capture of the Shield Trophy. In they're first cup game, Shelbourne continued their success from their last IFA cup game, with victory over Belfast side, West Ham. They went out that year to the eventual winners St. James Gate. The following season saw Shelbourne as firm favourites for the cup. Players such as the legendary "Boxer" Foley, who had won the cup 3 years previously wanted to get their hands on their first cup in the League Of Ireland but Belfast's Alton Town ensured that did not happen, beating the Reds 1-0. Shelbourne once again reached the final in 1925, but this time, were beaten by their biggest rivals, Shamrock Rovers in front of 23,000 in Dalymount Park. A year later, Shelbourne became league champions, with two points to spare over their Ringsend Rivals.
Shels topped the league again in 1929 and 1931, but the cup still eluded them. However, Shelbourne lost their league status, for the first and only time, in 1934. They were accepted back in to the league two years later and eventually won the cup in 1939. The sixties was a great decade for Shelbourne. Having one the league three times since the last cup success (1944, 1947 and 1953) Shelbourne started the sixties by winning their second ever FAI cup final in 1960.