He succeeds Marc Wilmots, who left his post last month, two weeks after the Euro 2016 quarter-final defeat by Wales.
The vacancy was advertised online by the Belgian Football Association.
It wanted a "strong and open communicator" who has a "proven track record in transmitting tactical and strategic knowledge" to top players.
In a statement, the Belgian FA said it was "delighted and proud to have found a coach at this level so quickly".
Martinez will hold a news conference at 11:30 BST on Thursday and his first match is against Spain on 1 September.
At Everton, Martinez managed Belgium internationals Marouane Fellaini, Romelu Lukaku and Kevin Mirallas.
source: BBC