According to Baseball-reference.com, the lowest ERA for one season in Major League history was a .8571 recorded by Tim Keefe, was was 23 at the time in 1880. However, because there were significant differences between the rules then and in the "modern era" of baseball, the generally accepted lowest ERA for comparison with any of today's players is Bob Gibson's 1.1225 in 1968, when he was 32. Again as a caveat, 1968 is referred to generally as the "year of the pitcher" because the height of the mound was lowered afterward, and the strike zone went from the bottom of the knee to the top of the armpit, until it was changed directly after the season. Bob Gibson won the NL Cy Young award for his efforts.
Tim Keefe of the 1880 Troy Trojans had a 0.86 ERA in 105 innings and is generally considered as having the lowest ERA in an MLB season as the 1880 season was only 84 games long. Since 1900, the lowest ERA belongs to Dutch Leonard of the 1914 Boston Red Sox at 0.96. He had a 19-5 record and threw 224 2/3 innings.
Dennis Eckersley. Eckersley pitched in 63 games for the Oakland Athletics in the 1990 season, had 48 saves, and an ERA of 0.61. He gave up 5 earned runs in 73 1/3 innings.
Dutch Leonard of the 1914 Boston Red Sox had an ERA of 0.96 in 1914.
In 1876, St. Louis had an ERA of 1.22 in 64 games. Since 1900, the record is held by the 1907 Chicago Cubs with 1.73 in 155 games.
Season: Bob Gibson of the St. Louis Cardinals at 1.12 in 1968. Gibson had 13 shutouts that season along with 28 complete games. Career: For pitchers that started their career after 1920, that is Mariano Rivera of the New York Yankees at 2.30 (as of June 30, 2009).
Duch Leonard with a .96 era.
Mariano Rivera's lowest ERA in a single season was 1.38 in 2005.
In 1914 Dutch Leonard had a 0.96 ERA
Tim Keefe of the 1880 Troy Trojans had a 0.86 ERA in 105 innings and is generally considered as having the lowest ERA in an MLB season as the 1880 season was only 84 games long. Since 1900, the lowest ERA belongs to Dutch Leonard of the 1914 Boston Red Sox at 0.96. He had a 19-5 record and threw 224 2/3 innings.
Johan Santana
Tom Seaver's lowest ERA in a single season was 1.76 in 1971. Seaver had a record of 20-10 with the New York Mets.
Jake Peavy of the San Diego Padres (2.54)
The club record is 1.69 accomplished by Nolan Ryan in the 1981 season.
Season record would be Spud Chandler
That was Pedro Martinez of the Boston Red Sox at 2.22.
Dennis Eckersley. Eckersley pitched in 63 games for the Oakland Athletics in the 1990 season, had 48 saves, and an ERA of 0.61. He gave up 5 earned runs in 73 1/3 innings.
Dutch Leonard of the 1914 Boston Red Sox had an ERA of 0.96 in 1914.