Elio Di Rupo, who heads the French-speaking Socialists in Belgium, is the leading candidate to become the country’s next prime minister.
His party won voting in the southern, Francophone region of Wallonia.
The French and Dutch-speaking Socialists could combine to form the largest group in parliament.
Di Rupo, 58, the son of Italian immigrants, would be Belgium’s first francophone premier since 1974.
With its leader Bart De Wever showing a willingness to build bridges, the victorious NVA looks set to reach out to the Socialists.
There were effectively two elections on Sunday. In northern Dutch-speaking Flanders, the separatist New Flemish Alliance or NVA emerged as the strongest party. It also won the most votes in the linguistically-divided country as a whole.
In Wallonia, the Socialists’ success sets the stage for it to provide the premier. In return, the party would be under pressure to agree to NVA demands for a devolution of power to the regions.