Peralta will report to Triple-A Pawtucket and could eventually offer some help at third base, a position the Red Sox have struggled to get production at all season.
Red Sox president of baseball operations Dave Dombrowski is familiar with both players, having also acquired them during his time with the Detroit Tigers.
Dombrowski had made a run at Fister earlier this season when he was a free agent, but the Angels were able to strike a deal with him first. Fister hasn't pitched in the Major Leagues yet this season, but he went 1-0 with a 4.02 ERA in three starts for Triple-A Salt Lake.
Fister will fill the fifth spot in the rotation, which has been a revolving door this season due to injuries. Fister will take the spot of Hector Velazquez, who has made two starts for Boston this season.
"One of our scouts, Eddie Bane, had seen him pitch before, recommended him, and felt he could pitch in the starting rotation at the Major League level," said Dombrowski. "We scouted by video his last outing. He became available, they decided not to add him to their Major League 25-man roster and we were in a position where we claimed him on the release waivers."
Once Eduardo Rodriguez (right knee subluxation) is ready to be activated at some point in the coming weeks, Fister could slide to the bullpen.
"A chance to add a proven Major League pitcher with a lot of experience," said Red Sox manager John Farrell. "A guy that we've gotten solid reports on with his recent starts while in Salt Lake City. I think more than anything, a guy that we can add some depth in the event that something unforeseen happens again from an injury standpoint."
Pitching for the Astros in 2016, Fister made 32 starts. He went 12-13 with a 4.64 ERA and 115 strikeouts in 180 1/3 innings. Fister's best season was '14 with the Nationals, when he went 16-6 with a 2.41 ERA.
Fister, an eight-year Major League veteran, and Peralta both played on the 2013 Tigers team that lost in six games to the Red Sox in the American League Championship Series. Red Sox righty Rick Porcello was also on that team.
Peralta was designated for assignment by the Cardinals on June 9 after posting a .204/.259/.204 slash line with no homers or RBIs in 58 plate appearances.
"We thought it was a nice fit for us," said Dombrowski. "He had other opportunities to go to places, but I talked to Jhonny -- and also, we go back -- and I thought that in our situation with Jhonny, he had a real good spring. Really didn't play very much in the beginning of the year, had some injuries. We had some mixed reports on him during the season, regular season. We felt it was an opportunity to go to Triple-A, take a look at him."
Pablo Sandoval was expected to be Boston's starting third baseman this season, but he has struggled with offense, defense and health and is on the disabled list for the second time this season. Josh Rutledge and Deven Marrero have recently been sharing time at third.
Peralta is a three-time All-Star, most recently in 2015, when he had 17 homers and 71 RBIs with the Cardinals.