The 35-year-old was a free agent as the Denver Broncos released him just two years after signing him in one of the most valuable trades in NFL history.
The Steelers then agreed to trade Kenny Pickett to the Philadelphia Eagles.
“I was fortunate to have several teams call, but this is where I wanted to be,” said Wilson of Pittsburgh, who have won a joint-record six NFL titles.
“To be a Pittsburgh Steeler, to wear the black and gold – it’s a true honour. The tradition, the history. There’s six [Super Bowl] trophies in there. We’ve got to go get a seventh.”