In Thursday's draw, captain Yannick Noah named Jo-Wilfried Tsonga, Lucas Pouille, Richard Gasquet and Pierre-Hugues Herbert for the three-day event in Lille.
Mahut, who has taken part in five of six ties since Noah became captain in 2016, and Benneteau had trained together this week.
Belgium will be led by David Goffin and Steve Darcis, with Joris De Loore and Ruben Bemelmans down to play Saturday's doubles.
Friday's first singles rubber will feature world number seven Goffin, who reached the final at the ATP Tour finals earlier this month, and Pouille.
Tsonga will then take on Darcis before Gasquet and Herbert face Bemelmans and Loore in the doubles.
The reverse singles rubbers will be played on Sunday.
Belgium have never won the title while France claimed the last of their nine wins in 2001.
(Reporting by Julien Pretot; Editing by William Maclean and John Stonestreet)
