Steward was chosen 188th overall earlier this month with the first of Buffalo's two sixth-round selections. He spent four seasons at Clemson, where he appeared in 43 games, including 12 starts.
Steward was a highly regarded prospect entering Clemson, but had his career slowed by injuries to both knees.
In Buffalo, he is expected to compete for a backup spot on defense, and make an immediate impact on special teams.
The Bills have now signed five of their six draft picks. Cornerback Ronald Darby, a second-round pick, is Buffalo's only unsigned rookie.
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