Hershiser replaces Oscar Acosta, who was fired after Thursday's loss to the Chicago Cubs. The Rangers have a team ERA of 5.05, the second-highest in the major leagues.
The main task for Hershiser will be working with Chan Ho Park, who signed a five-year, $71 million contract with the Rangers in the offseason and is just 2-3 with a 9.40 ERA in eight starts.
Hershiser, 42, spent much of his career in the Los Angeles organization and has a long-standing relationship with Park, who was with the Dodgers until this season.
Hershiser joined the Rangers last fall as a special assistant to general manager John Hart. He has no previous coaching experience but posted a 204-150 record and a 3.48 ERA in an 18-year career that included stints with the Dodgers, Cleveland, San Francisco and the New York Mets.
He won the National League Cy Young Award and the World Series Most Valuable Player Award with the Dodgers in 1988. He worked in the postseason as recently as 1999 with the Mets.
Acosta was in his first season as Rangers pitching coach and was believed to have a strained relationship with manager Jerry Narron. But another starter, Kenny Rogers, praised Acosta.
"I got along with him, understood where he was coming from and agreed with his methods," Rogers told the Fort-Worth Star Telegram.
Hershiser will assume his duties immediately. The Rangers continue an interleague series with the Pittsburgh Pirates on Saturday night.