The 26-year-old from Guyana replaced leg-spinner Devendra Bishoo while middle-order batsman Kirk Edwards, who was in the squad for the second Test which ended in a draw at Trinidad on Thursday, was not considered for selection because of a leg injury.
Fudadin was called up after making 576 runs at an average of 48 in a recent regional tournament.
"Fudadin has been a member of the West Indies A Team for a while now and we have seen signs of development and improvement," West Indies chairman of selectors Clyde Butts said.
West Indies captain Darren Sammy said he did not expect any changes for the third Test although there was some concerns about fitness of fast bowler Fidel Edwards.
"So far we've been using the same combination and it's worked for us," Sammy said.
"Fidel has a slight pain in his back so we'll monitor that. If not then Ravi (Rampaul) comes in and I know Ravi will do the job for us."
Sammy also said he had spoken with Bishoo and reassured him that he would get another chance.
"We just had a team talk and what I said to Bishoo was he's been a warrior to us, especially last year, but sometimes you lose form," Sammy said.
"I told him I know deep down he will come back stronger because that's the sort of player he is."
Darren Sammy (Captain), Adrian Barath, Carlton Baugh, Kraigg Brathwaite, Darren Bravo, Shivnarine Chanderpaul, Narsingh Deonarine, Fidel Edwards, Assad Fudadin, Kieran Powell, Ravi Rampaul, Kemar Roach, Shane Shillingford