Harvey was 3-5 with a 7.09 ERA in 12 starts. He gave up 6 runs, 7 hits and 5 walks over 6 innings in a 6-2 loss to the Houston Astros on Thursday night.
"The decision was made because we felt like it would increase our chance of winning games," Angels manager Brad Ausmus said after discussing the move with general manager Billy Eppler. "Matt was a very well-liked teammate, a guy that everyone pulled for, including myself. But we're in the business of winning baseball games. In talking to Billy, we just felt like this was the best move to make in order to help us win games."
Once dubbed "The Dark Knight," Harvey was among baseball's most dominant starters for a time with the New York Mets. He started the 2013 All-Star Game at Citi Field but hurt his elbow later that summer and never consistently regained his 98 mph fastball or command following Tommy John surgery.
Harvey lost his spot in the Mets' rotation after four starts last year and had a 10.50 ERA in four relief appearances. When he refused to accept a minor league assignment, the Mets traded him to the Cincinnati Reds. Harvey went 7-7 with a 4.50 ERA in 24 starts for the Reds, became a free agent and signed with the Angels.
He did not pitch for Los Angeles between May 23 and July 13 because of a strained back, and his fastball velocity averaged 92 mph in two starts after his return. He gave up 48 runs and 63 hits in 59 innings this season with 39 strikeouts and 29 walks.
"He's not throwing 97, but he's not throwing 89 either," Ausmus said. "He's got four pitches. He's got the stuff to get major league hitters out. He just has to find a way to harness it."
The Angels called up right-hander Jaime Barria from Triple-A Salt Lake City before the series opener against the Seattle Mariners on Friday. Barria struggled in his return to the majors, giving up 10 runs on nine hits in 3 innings of relief as the Angels lost 10-0.
The Associated Press contributed to this report.