The Brazilian defender has not figured for the Blues since January 20.
He has not started a Premier League game since a meeting with Bournemouth on October 28, with the Blues favouring other options.
Luiz has, however, been reinstated for a trip to Vicarage Road which will see Chelsea looking to reclaim third spot in the Premier League table.
Chelsea team: Courtois; Azpilicueta, David Luiz, Cahill (c); Moses, Bakayoko, Kante, Zappacosta; Willian, Hazard, Pedro.
Subs: Caballero, Rudiger, Emerson, Drinkwater, Fabregas, Hudson-Odoi, Giroud.
While Luiz has made the starting XI, January signings Olivier Giroud and Emerson have had to settle for spots among the substitutes.
The former would have been hoping to start, with Alvaro Morata ruled out and regular game time denied him at Arsenal, but the Frenchman finds himself in an all too familiar position.
He proved to be a useful impact option while with the Gunners, and that is how Conte will be utilising him against Watford.
If the Blues are in need of inspiration from off the bench, then they also have Cesc Fabregas and Danny Drinkwater at their disposal.
A positive result of some kind is a much for Conte, with the Blues boss having fallen under increased pressure on the back of a 3-0 defeat at home to Bournemouth last time out.