He had an even 47–47 record over six seasons as a starting pitcher in the Indians' farm system when he received a September call-up in 1974.

He was 1–2 with a 4.79 ERA as a starter when the Indians traded Gaylord Perry to the Texas Rangers for Jim Bibby, Rick Waits, Jackie Brown and $100,000 on June 13.

In order to make room on the major league roster for the two additional pitchers acquired, Kern was optioned to the triple A Oklahoma City 89ers.

[4] Recalled in late June, he strained a muscle in his shoulder in July and sat out the remainder of the season.

Early in the 1977 season, the Indians traded closer LaRoche to the California Angels, opening the door for Kern to inherit the job.

He was 10–2 with a 1.48 ERA and sixteen saves at the 1979 All-Star break to earn his third consecutive selection to the AL squad.

AL manager Bob Lemon pulled Kern in favor of New York Yankees ace Ron Guidry.

[12] Kern was named the American League pitcher of the month for May 1979 going 4–0 with four saves, striking out 31 in 14 games and posting a 0.61 ERA.

At the 1981 Winter meetings, he was traded to the New York Mets for Dan Boitano and Doug Flynn,[17] however, before he could make an appearance with his new club, he was packaged with Greg Harris and Alex Treviño, and sent to the Cincinnati Reds for slugger George Foster.

Kern pitched respectably in Cincinnati, in 1982 going 3–5 with a 2.84 ERA and two saves, however, he was unhappy with the Reds' rule against facial hair, and asked to be traded.

[20] Kern accused the White Sox of using him improperly by asking him to throw in a game after an injection, causing him to tear two tendons.

Kern signed a minor league deal with the Milwaukee Brewers shortly afterwards and was called up that September, appearing in six games without giving up a run.

[27] Kern is an outdoor enthusiast, and in 1987, he started the Emu Outfitting Company, which was named after his major league nickname, the "Amazing" Emu [28] in Arlington, Texas, an outdoor adventure company that books and operates hunting, fishing, and photographic trips in North and South America.