Howell, 29, had a 3.04 ERA in 50 1/3 innings last season out of the bullpen with the Tampa Bay Rays. He had success against left-handed hitters, who batted a mere .200 against him.
The reliever spent seven seasons with the Rays, posting a 21-22 record with 21 saves and a 4.42 ERA.
Howell joins Brandon League as the second major addition to the Dodgers' bullpen this offseason. League agreed to a three-year deal worth $22.5 million in November.