Bonilla, 26, was designated for assignment by the Pirates last Thursday to clear a roster spot for pitcher Pat Light. The Pirates had signed him to a one-year, $575,000 contract back in November.
The right-hander hasn’t pitched in the majors since 2014 and spent last season in the Dodgers’ minor league system. Between Double-A Tulsa and Triple-A Oklahoma, Bonilla posted a 3.97 ERA with a 118/40 K/BB ratio over 111 innings.
Bonilla is likely to pitch out of the Reds’ bullpen in a long relief role assuming he makes the 25-man roster, but he could eventually move into the rotation if the need arises.