Kelly moved from Quincy to Lakeland in 1949, and four years later, was elected to the city commission.

Kelly won two terms as mayor of Lakeland before unseating Republican state senator Harry King in 1956.

Kelly left the state senate in 1963, and began campaigning for the Democratic gubernatorial nomination, which he lost to Haydon Burns.

[2] Kelly ran in the Florida primary of the 1968 Democratic Party presidential primaries, placing third behind Senator George Smathers, who was running as a stand-in candidate for Vice President Hubert Humphrey, and Senator Eugene McCarthy.

Kelly represented the unpledged delegates who did not want to be pledged to a candidate at the 1968 Democratic National Convention.