Monfils won his seventh ATP World Tour singles title at the 2018 Qatar Open. He had lost his previous three Qatar Open singles finals. Appearing in the 2018 edition of the tournament as an unseeded wildcard, he advanced to final via walkover after top seed Dominic Thiem had to withdraw from their match in the semifinals because of illness. In the final, he defeated Andrey Rublev 6–2, 6–3 in 61 minutes. In his next tournament, the 2018 Australian Open, Monfils lost to the no. 14 seed Novak Djokovic in four sets in the 2nd round. Monfils then made the semifinals of the 2018 Argentina Open, upsetting 7th seed Pablo Cuevas in the first round before being handily defeated by Dominic Thiem in the semifinals. Continuing his South American swing, Monfils played two stunning matches during the 2018 Rio Open. In round one, Monfils completed a significant comeback to beat Horacio Zeballos, saving one match point in the process with a booming forehand. In round two, the Frenchman pulled off an even bigger stunner, defeating top seed and world number 3 Marin Čilić in a match that stretched over two days due to inclement weather. The match was halted at 6–3, 6–6 (7–7) in Monfils' favor, a stoppage that surprised many. Monfils lost his quarterfinal match against Diego Schwartzman in straight sets.
He was coached by countryman and former ATP pro Thierry Champion (since September 2004) but they parted company in September 2006. Nevertheless, Monfils's fitness trainer is still Rémi Barbarin. Monfils announced a partnership with a new coach, Tarik Benhabiles, in May 2007. However, for the 2008 season, Monfils hired Roger Rasheed as his coach. In 2011, Monfils parted ways with Rasheed and announced that his fitness coach, Patrick Chamagne would take the reins as his new full-time coach. That lasted until 2013. As of the 2015 French Open, Monfils shares coach Jan De Witt with fellow countryman Gilles Simon. On 15 November 2012, Monfils split with his coach.