Kirkman will be invited to spring training with a chance to make the big club, the same situation Lewis was in last season. Kirkman, who was out of options, wasn't tendered a contract by Tuesday's deadline, allowing him to become a free agent.
In 36 games for Triple-A Round Rock, Kirkman went 5-5 with a 4.47 ERA. After getting called up to the Rangers, he pitched in 12 games, going 0-1 with a 1.59 ERA.
The Lewis signing, which is worth $4 million, gives the Rangers 38 on the 40-man roster.