Sunderland and Crystal Palace spent much of deadline day locked in a tug-of-war for the Belgium international, with two private jets waiting at Lyon's airport as Fofana weighed up which club to join.
Sunderland owner Kyril Louis-Dreyfus travelled to France in person to press the club's case, while Palace's interest was driven partly by manager Pierre Sage, who previously worked with the winger at Lyon. In the end, Fofana chose Wearside, with the transfer completed for a fee in the region of €30m plus around €5m in add-ons.
The move brings down the curtain on a spell in which the 21-year-old developed into one of Ligue 1's most eye-catching wide players.
He arrived from Gent in January 2024 and, despite a campaign disrupted by ankle injuries last season, had started this season strongly, scoring important goals against Toulouse and Fenerbahçe before the transfer saga unfolded.
Fofana marked his departure with a heartfelt message to supporters on social media.
"After several years wearing the colours of Olympique Lyonnais, it's time for me to open a new chapter in my career," he wrote. "I want to sincerely thank the club, my teammates, the staff and everyone who supported me during this adventure.
"A big thank you also to the fans for their support, their passion and all the moments we shared together at the stadium. Wearing this shirt and representing OL has been a great source of pride. I will keep many happy memories from this period, and real gratitude for everything the club has given me. Thank you for everything, Lyon."
The sentiment appeared to be mutual, with Fofana widely regarded as one of the more popular figures among Lyon's support in recent seasons. His exit leaves the club losing one of their most valuable offensive assets, though the fee recouped will provide useful funds as Lyon look to reshape their squad following a turbulent period that included a brief relegation to Ligue 2 before their return to the top flight.
Sunderland's pursuit reflects the scale of their ambition following promotion back to the Premier League, with the Black Cats determined to add proven attacking quality capable of making an instant difference. Fofana will now have to settle quickly into English football, having contributed 13 goals and 10 assists in 98 appearances across his time at Lyon and Gent.