Roberts spent two-and-a-half seasons on loan with Celtic between 2016 and 2018, contributing 18 goals and 26 assists in 78 first-team appearances, and helping the side win seven trophies, including three consecutive league titles.
The 24-year-old was a popular figure during his time at Parkhead but his career has failed to ignite since, making just a single first-team appearance for Man City, and spending most of his time on loan at clubs including Girona, Norwich, Middlesbrough, Derby County and Troyes.
Roberts has joined Sunderland on a permanent deal until the end of the season with the option of an extension and could make his debut against Portsmouth at the Stadium of Light on Saturday.
Roberts told the Sunderland website: “I can’t wait to get going. I came to the game against Sheffield Wednesday a few weeks ago to get a feel for it and it was great to watch – and something that I wanted to be a part of. The fans want you to do well and work hard every matchday and that pressure and expectation is something I thrive off. I just want to do well for the people that support me and get Sunderland back to where they belong.”
Sunderland boss Lee Johnson added: “Patrick is a player that we have always kept our eyes on over the years because he really is a top talent. This is an amazing opportunity – for him and the club – to give him the love he requires at a standard whereby we think he can excel and then come with us to the next level. He thrives on the big occasion and the beauty of Sunderland is that there is a big occasion every three days. We hope that this is the place he calls home for a number of years.”