[6] Pitching for the Lancaster JetHawks of the High-A California League in 2014, Hader and two relief pitchers combined to throw a no-hitter on May 13.

[7] After pitching to a 9–2 record with a league-leading 2.70 ERA and 112 strikeouts in 103+1⁄3 innings, the Astros promoted him to the Corpus Christi Hooks of the Double-A Texas League in August.

[10] On July 30, 2015, the Astros traded Hader, Brett Phillips, Domingo Santana, and Adrian Houser to the Milwaukee Brewers for Carlos Gómez and Mike Fiers.

[13] Hader began the 2016 season with Biloxi, and made his first start for the Colorado Springs Sky Sox of the Triple-A Pacific Coast League on June 12.

[21][22] After giving up a single to Boston Red Sox baseman Mitch Moreland, Hader was replaced after 26 pitches, allowing four hits and one out over five batters.

Among MLB pitchers who threw at least 20 innings, Hader held left-handed batters to the lowest batting average (.088).

Hader began the 2019 season as the Brewers' closer following injuries to fellow relievers Jeremy Jeffress (shoulder strain) and Corey Knebel (Tommy John surgery).

[27] In the 2019 National League Wild Card Game, Hader blew the save for the Brewers, giving up a three-run single to Juan Soto of the Washington Nationals, which, coupled with an error from right fielder Trent Grisham, led to Washington's go-ahead run scoring on the play and resulted in the Brewers eventually losing the game.

[29] Hader began the 2020 season with 12 consecutive hitless appearances, the longest such streak in major league history.

[31] For July, Hader was named NL Reliever of the Month, the fourth time he won the award.

[32] On September 11, Hader pitched the ninth inning to close out a combined no-hitter against the Cleveland Indians.

After beginning the 2022 season with 25 saves in 27 appearances and a 1.05 ERA, Hader’s pitching declined during the summer, and on August 1, the Brewers traded him to the San Diego Padres for Taylor Rogers, Dinelson Lamet, Esteury Ruiz, and Robert Gasser.

[38] Hader was named the NL Reliever of the Month for April after recording 10 saves and holding opposing batters to a .093 batting average while allowing only one run in 13.0 innings pitched.

[42] On August 10, 2024 versus Boston, Hader converted his 25th consecutive save opportunity, surpassing Brad Lidge's franchise record of 24,[43] and extended that streak to 29 total.

[46] Hader made 71 regular season appearances in 2024, posting an 8–8 record, 3.80 ERA, 71 innings, 43 hits, 12 home runs, and 25 walks surrendered and 105 strikeouts.

[50] During the 2018 Major League Baseball All-Star Game, a series of tweets by Hader ranging from mid-2011 to late-2012 were discovered to contain racist, homophobic and sexist content.