The 22-year-old joins on a loan deal until the end of the season with the Parkhead club having an option to make the deal permanent.
Jota, a Portuguese Under-21 international, follows Greek striker Giorgos Giakoumakis in the door on transfer deadline day at Celtic, becoming the 11th summer signing as Ange Postecoglou overhauls his squad.
The player spent part of last season on loan at Real Valladolid, while he helped Benfica win the Primeira Liga in 2019.
He said: “I am very happy to join such an historic and exciting team as Celtic. Having played in Portugal and Spain, everyone knows that Celtic is a huge name across Europe and a club with real heart and soul.
"It will be a pleasure and an honour to fight for this club and I can’t wait to feel the atmosphere from our supporters at Paradise. I know the Manager wants us to play fast, attacking football, the way it should be played and I can’t wait to play my part in this.
“I will work hard to do all I can to make the fans happy and enjoy some good times together.”
Meanwhile, Ryan Christie has departed, completing a £2.5million move to English Championship side Bournemouth.
“He was being courted by a number of Premier League clubs, so it is a huge coup to have signed him,” the Cherries’ chief executive Neill Blake said.
“We think it speaks volumes about him as a player and us as a club that he chose to come here and work under Scott Parker and his staff.”