There were fourteen Democratic candidates for Lieutenant Governor going into the convention. Before the balloting began, three candidates (
New Bedford Mayor Edward F. Harrington,
Lowell City Councilor George P. Macheras, and former state representative Rico Matera) withdrew. On the first ballot,
Massachusetts Governor's CouncilorJohn W. Costello led with 428 votes to Worcester attorney and Industrial Accident Board member
Joseph E. McGuire's 404, state senator Mario Umana's 250, and state representative Joseph G. Bradley's 112. The other seven candidates (James A. DeGuglielmo, Harold L. Vaughn, Boston school committee member
Thomas S. Eisenstadt, state comptroller Joseph Alecks,
Holyoke mayor Daniel F. Dibble, and state representatives Andre R. Sigourney and George H. O'Fannell.) received less than the 100 votes required to remain on the ballot and Bradley chose to drop out, which left Costello, McGuire, and Umana as the only remaining candidates. Costello led again on the second ballot, with 641 votes to McGuire's 600 and Umana's 343, but did not receive enough votes (733) to win the nomination. The same happened on the third (687 votes for Costello to McGuire's 656 and Umana's 172), however on the fourth ballot, Umana fell to 99 votes, which eliminated him from the contest. On the fifth and final ballot Costello won the party's endorsement by defeating McGuire 724 votes to 691.