The 26-year-old right-arm bowler has played nine one-day and 10 Twenty20 internationals for Ireland, and was previously on the books at Sussex.
He will appear for Hampshire's second XI against Somerset on Monday.
Hampshire are currently suffering an injury crisis in their bowling department, with Fidel Edwards, Reece Topley, Gareth Berg and Ryan Stevenson all unavailable.
Hampshire have signed Ireland seamer Craig Young on a short-term loan deal.