The Marlins activated Simpson (elbow) from the 60-day injured list and optioned him to Triple-A Jacksonville on Tuesday.
The left-hander had the elbow issue surface in February and underwent surgery to repair the ulnar nerve in late April, but he's been fully cleared after an eight-appearance rehab assignment. Simpson surrendered six runs with an 11:8 K:BB across 8.2 innings during the rehab stint, so he'll be sent to Triple-A rather than joining Miami's bullpen.