The league began its first season on May 16, 2006 with six teams: the Alexandria Aces, Amarillo Dillas, Edinburg Coyotes, Laredo Broncos, Rio Grande Valley WhiteWings and San Angelo Colts. The San Angelo franchise previously played in the now-defunct Central Baseball League, while the Amarillo Dillas previously played in the now-defunct Texas-Louisiana League. The United League was originally owned by an investor group, United Sports Equities, which listed Bradley Wendt as CEO and Managing Director, his brother Gary Wendt and former congressman John Bryant as Principals, and Byron Pierce as COO. The ULB filed for Chapter 11 Reorganization in January 2009 amid allegations of fraud and financial mismanagement by Bradley Wendt and defaults on stadium leases by Brad Wendt and was ultimately forced into Chapter 7 by John Bryant who along with Pierce now control the league.
The San Angelo Colts announced on July 2, 2014 that it had filed for Chapter 11 bankruptcy protection. Although it was stated at the time that operations would not be affected, the team announced on August 11, 2014 that the final 8 games of the 2014 regular season would not be played. Originally scheduled to end August 24, the league's 2014 regular season ended August 15, with the best-of-five championship series between the Cats and the WhiteWings starting August 16. The United League Baseball is looking into possibly expanding to Del Rio, Texas and is schedule to meet with city officials in October 2014.
In November 2014 it was announced that the City of Ft. Worth has not renewed the lease at LaGrave Field for the Ft. Worth Cats, thus leaving them without a home for the 2015 season.
Format: for the 2010 season the United League playoffs consisted of 4 teams competing in 2 rounds, with the top 4 regular season teams making the playoffs. In the first round the regular season champion faced the 4th seed while seed 2 faced seed 3 in the best of 3 series. The winners then advanced to the championship best-of-five series.
Format: for the 2009 season the United League playoffs consisted of 4 teams competing in 2 rounds, with the top 4 regular season teams making the playoffs. In the first round the regular season champion faced the 4th seed while seed 2 faced seed 3 in the best of 3 series. The winners then advanced to the championship best-of-five series.
Format: for the 2008 season the United League playoffs will consist of 4 teams competing in 2 rounds. In the first round the top two teams at the end of the first half of the season will host the two remaining teams with the best overall winning percentage throughout the season in a best-of-three series. The winners then advance to the championship which will be played at both parks, with the lower seed hosting game one and the higher seed hosting games two and three of the best-of-three series.
Format: for the 2007 season the United League played in a split season format, crowning a first half champion and a second half champion. The champions then played for the ULB Championship. If one team was to win both halves, the team with the second-best overall season record would have qualified for the playoffs as a wild card. The championship series was the best 4 out of 7 games, to be played home and away in a 2-3-2 site format, with home field advantage awarded to the first half champion.
Format: for the 2006 season the top four teams in the regular season standings made the playoffs, including the regular season champion and 3 wild card teams. The playoffs then commenced with two rounds of games to determine the United League champion:
United League Baseball hosted an annual All-Star Game which rotated host cities throughout the league. Its format in 2008 featured the United League all-stars versus the Golden League all-stars. In 2006 the first All-Star Game pitted the best team against the all-stars from the rest of the United League. In 2007 the second All-Star Game pitted Team North (All-Stars from Alexandria, Amarillo and San Angelo) against Team Rio Grande (All-Stars from Edinburg, Laredo and Rio Grande Valley).
The ULB's all-star festivities are a two-day event, the first day featuring various celebrations and recognitions, followed on the second day by the Home Run Derby and the All-Star Game.