The Citizens League was formed in San Antonio after the Wurzbach-McCloskey 1928 congressional election contest. Harry McLeary Wurzbach, the Republican incumbent who had served three terms in the United States House of Representatives, was apparently defeated in 1928 by Augustus McCloskey, the Democratic nominee who had been supported by the San Antonio city political machine. After thirteen months Wurzbach was declared the winner in the disputed election, and he replaced McCloskey in the House. The league, founded by prominent citizens, declared itself against "machine rule" and demanded honest elections, honest spending of bond proceeds, only two terms for officeholders, and an end to organized gambling. The league won most county offices in the Democratic primary in 1930, but in 1931 it failed to capture city hall; the machine's virtual monopoly of the Latin American and African American vote was an insuperable barrier. In 1932 the league again won a sweeping victory in the county races; African Americans did not vote in the Democratic primary.
Internal dissension in the league and the death of its chief target, Mayor C. M. Chambers, combined to defeat its ticket in the 1933 city election. The weakened league rallied in 1934 to win most of the county offices, losing its district attorney, Walter Tynan, but sending its tax assessor, Fontaine Maury Maverick, to a new congressional seat. In 1935 its candidate for mayor withdrew after the campaign was under way, and the league then withdrew the rest of its candidates. In 1936 the executive committee, then nine in number, quarreled over whether it should oppose its incumbent sheriff for not closing the gambling houses. By a vote of five to four the sheriff was placed on the ticket, but the four dissenters resigned and withdrew, three of them doing so publicly. Only Maverick and a few minor candidates survived the machine landslide. While in theory the league consisted of a convention of all of the citizens of San Antonio, in practice the executive committee determined policy in campaigns and nominated candidates, and the officeholders ran the league between elections. The six campaigns waged by the league featured nightly rallies designed to carry the campaign to every part of town. While the executive committee was always conservative politically, the league's best-known product, Maverick, was an unqualified liberal.