Foster took to Instagram on Wednesday morning, saying of his contract, "Not a bad career so far for an undrafted kid out of Tennessee (Go Vols). #SteelerNation Let's get it O Line."
Terms were not immediately available. Foster just completed a three-year contract, and now he gets another one.
He is the third Steelers player who was set to become an unrestricted free agent but decided to re-sign with the team, joining receiver Darrius Heyward-Bey and cornerback William Gay.
Foster, 30, earned his $1.85 million salary last season, playing every offensive snap for the Steelers. The only other player to do that was guard David DeCastro. Foster has started 87 games for the Steelers, who signed him as an undrafted free agent in 2009.
Foster held up well in his seventh season, helping the Steelers generate a top-10 rushing offense for much of the year despite several injuries on the line and at running back.
Foster, who is considered a great locker room guy, has spent his entire career with the Steelers and entered free agency with the attitude that he wanted to stay, but said he was curious how the market would assess his value.