Hartlieb was claimed off waivers by the Mets on Thursday, Jason Mackey of the Pittsburgh Post-Gazette reports.
Hartlieb was designated for assignment by Pittsburgh on Saturday, but he'll land another spot on a 40-man roster going forward. The right-hander could report to Triple-A Syracuse to begin his time with his new organization, but he's made four relief appearances in the majors this year and could return to the big leagues as a low-leverage bullpen option at some point.