The association said in a statement on Friday that it had confidence in the Spaniard after he steered Belgium to the World Cup with nine wins and one draw.
Martinez, who previously managed English Premier League club Everton, will name his 23-man World Cup squad on Monday.
The football association added that the contract was extended for two years under the same conditions as when signed in 2016, without giving details. Belgian media have said Martinez was earning 1 million euros ($1.18 million) per year.
His assistants, Graeme Jones and Richard Evans, have also signed up for a further two years. There was no news about former France striker Thierry Henry, who has also been working as an assistant to Martinez.
Belgium are drawn in Group G in Russia 2018, where they will play Panama, Tunisia and England.
(Reporting by Philip Blenkinsop; Editing by Hugh Lawson)
