The Oscar winner, 65, joined the bridal party for photos outside the Fairmont Hotel in downtown Pittsburgh as they were getting ready to leave for the ceremony on Saturday.
The bride, Grace Gwaltney, revealed she was shocked to see the Finch star.
"He was like, 'Hey! I'm Tom Hanks. I would love to get a photo with you' and I immediately froze and was just looking around," she told KCRA. "I didn't know what to do."
The wedding photographer Rachel Rowland told the Pittsburgh Post-Gazette that the group "started screaming and were pretty much in shock" after the encounter.
This is amazing! Haha.