When he returned home from his army service in 1919, Lawrence was elected as chairman of the Allegheny County Democratic Party. At the time, Pittsburgh was a Republican bastion, with Democrats holding wide support only in the lower class and among recent immigrants, who were concentrated in industrial jobs. With the help of Joe Guffey, a future Pennsylvania Senator, Lawrence led the rising Pennsylvania Democratic party that would soon dominate local and statewide politics. In the 1928 presidential election, Lawrence worked hard for Alfred E. Smith from New York, another Irish Roman Catholic politician who had also risen from the slums without the benefit of a formal education. The vicious anti-Catholic campaign that defeated Al Smith that year had a profound effect on Lawrence. He believed that Roman Catholicism was an insurmountable handicap in United States presidential politics. Consequently, at the 1932 Democratic National Convention, Lawrence deserted Al Smith's presidential campaign and delivered the Pennsylvania delegation to Franklin D. Roosevelt, solely because of his fear of the religious issue.