The Mexican was a Force India Formula 1 development driver last year, participating in six Friday practice sessions at grands prix, and claimed his maiden FV8 3.5 podium at Spa-Francorchamps.
He tested Fortec's FV8 car last month and was fastest in the first Jerez session.
"They were my number one choice of team for 2017 and I look forward to sharing great success with them next season," said Celis, who is the first driver to be officially confirmed in the 2017 FV8 field.
He previously drove for Fortec in 2013, completing a Formula Renault NEC season plus occasional Formula 3 outings.
Fortec's FV8 3.5 team manager Jamie Dye added: "It is great to have 'the Fonz' back with us.
"We had a great year of 2.0 together in 2013 - he is a great kid.
"We had a good test in the 3.5 car recently, so we are ready to take on the championship in 2017."
Although Fortec's Celis news is the first official driver announcement, teams in the renamed World Series Formula V8 3.5 category are reporting higher interest than at this time 12 months ago.
In its second season without Renault support, the series has revamped its calendar to go outside Europe and partner with the World Endurance Championship for six of its nine rounds.
The 2015 Formula Renault 3.5 season will be notable for being the last with the French company's backing but also produced a worthy champion in Oliver Rowland. PETER MILLS evaluates this year's crop of drivers
Last year's field was extraordinary and hard to match, but the Formula Renault 3.5 grid will still have plenty of talent this season. Glenn Freeman runs through the field ahead of this weekend's season opener
Landing the Fortec seat that took rising star Robin Frijns to the 2012 FR3.5 title was already a good sign for Stoffel Vandoorne. Then McLaren took him under its wing. Peter Mills tells Vandoorne's story so far