Mina, who was linked with a move to Manchester United for much of the window, arrives a the club in a £30 million deal, providing boss Silva with the defensive lynchpin he has been so desperately craving.
Mina, for whom Barca have retained a buy-back option, said the chance to play alongside Gomes and Lucas Digne - who made the same switch last week - played a part in his decision to join Marco Silva's men.
The 23-year-old Mina, who was impressive in defence at this year's World Cup in Russian Federation where he also scored three goals, will rejuvenate an ageing Everton back line while offering a threat from set-pieces at the other end of the pitch.
During negotiations for Mina, Everton were offered Gomes on a season-long loan, the Portugal midfielder having struggled at Barcelona since his €35m (£31.5m) arrival from Valencia two years ago.
Several Premier League sides including West Ham and Chelsea had been in the hunt for the Brazilian winger while AC Milan also expressed an interest.
Everton have announced that Mina will be No 13 while Andre Gomes will be No 8.
'They are historically among the four most successful clubs in England and when I found out about the club and what the manager wanted from me, I was happy. "I am also determined to do my best for Everton". But I was also convinced Everton could improve me and that I would be able to show my best as a player here'.
Moments later they also confirmed that Portugal global Gomes would join the Premier League side on loan.
"Every discussion we've had was very important in making me feel his confidence about my game".