Allen resuscitated his career in Pittsburgh last season after Dallas released him, and he provides a bit of a safety net in the secondary with the Steelers unlikely to re-sign Ryan Clark.
Allen worked his way into the role of third safety after returning to the Steelers, and he played extensively in the quarter package. His signing follows a report by ESPN NFL Insider Adam Schefter that the Steelers won't consider releasing Pro Bowl safety Troy Polamalu as they work to get in compliance with the salary cap.
Allen recorded 42 tackles in 12 games last season, and his interception in a November game against the Lions helped preserve Pittsburgh’s 37-27 win over Detroit.
The 10th-year veteran is also a core special teams players providing the Steelers value on another front.
Shamarko Thomas, whom Allen supplanted in the quarter package last season, could get the first crack at replacing Clark, who has started at free safety since 2006. He and Allen could share time at the position, and the Steelers are expected to draft at least one safety they can develop.
Allen is the second impending free agent to re-sign with Pittsburgh.
Outside linebacker Jason Worilds signed a one-year, $9.54 million contract on Tuesday, one day after the Steelers placed the transition tag on the fourth-year veteran.