Former Belgium boss Martinez succeeds Fernando Santos, whose eight-year reign came to an end after the Qatar World Cup.
It concluded a famous era for the Selecao, including the Euro 2016 triumph and victory in the Nations League in 2019.
“A new leader at the service of Portugal – welcome Mr Roberto Martinez,” read a tweet from the Portuguese national team account on Twitter.
At the presentation ceremony of the new National Squad in Cidade do Futebol, the President of the Portuguese Football Federation, Fernando Gomes, welcomed the new coach and highlighted his competence.
Martinez, previously manager at Everton and Wigan, was himself available after his spell with Belgium ended after the tournament in Qatar.
A group stage exit ensured a disappointing finish to his time in charge of the Red Devils.
Morocco and Croatia progressed from Group F with Belgium third ahead of Canada.
The high point of Martinez’s time in international football came when Belgium finished third at the 2018 World Cup, beating England in the third-place play-off in Russia.
Martinez inherits a squad with enormous potential after defeat to Morocco in the last eight in Qatar.
It remains to be seen what Martinez will do with veteran star player Cristiano Ronaldo, who was dropped last month as Portugal plotted a route to the final.
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