Ramirez, 31, hasn't pitched in the Major Leagues since 2009, when he appeared in 19 games for the Royals. A starter early in his career with the Braves and also with the Mariners in 2007, Ramirez is 39-35 with a 4.64 career ERA in 157 games, 105 as a starter.
The Angels optioned right-hander Michael Kohn to make room.
"I got a call from K.J. [Keith Johnson], the manager down in Salt Lake, at about 10 in the morning," Ramirez said. "He told me to pack my bags. I asked him where I was going. He says, 'You're going up.'
"I was very happy. Last couple years for me have been kind of a little rough. I thank God for the opportunity the Angels gave me by signing me in the spring and for calling me up."
One of Ramirez's objectives will be to avoid the leadoff walks that have plagued some Angels relievers.
"I just want to come in here and do what I've been doing the last three months," he said. "That's kind of attacking the zone, throwing strikes, that's about it. Just kind of keeping it simple -- throwing the ball to the glove."
Ramirez joins Scott Downs and Hisanori Takahashi as the lefty complement in the bullpen.
"Ramirez has some Major League experience," Angels manager Mike Scioscia said. "He's been pitching well in Triple-A. From the left side, we'll have a lot more matchups. He's more than [situational]. He's got a fastball, cutter, changeup. He throws strikes."
In 39 appearances with Salt Lake, one as a starter, Ramirez was 3-1 with a 3.47 ERA. He had six saves and a 1.26 WHIP in 46 2/3 innings.