He takes the roster spot of Keeon Johnson, who suffered a broken foot that needed surgery during Thursday's practice. Johnson and Severin were teammates at the University of Virginia.
Johnson, a rookie who went undrafted, flashed in recent weeks at Giants training camp. His size and strength (6-3, 216) was noticeable and he was using that frame to make contested catches in the air. But he broke the fifth metatarsal in his foot Thursday and was carted off the field. He had surgery that night.
Severin, 24, spent all of last season with the Steelers on injured reserve. He was released earlier this week after catching two passes for 24 yards in the preseason opener against the Giants.
The Steelers are loaded at wide receiver after the return of Martavis Bryant and needed to make room on their roster.
Severin (6-2, 205) has good size, but he becomes a longshot to make the Giants roster by joining the team in mid-August. It's unlikely he's ready to play on Monday Night Football against the Cleveland Browns, which leaves him with approximately two weeks and two preseason games to make a strong impression.