Thursday's meeting in the Belgian capital will be the first time that Rajoy has entered a European summit with such a clear mandate from across the national political spectrum.
Spain's cross-party resolution on the position the country would take at the crucial summit received overwhelmingly backing, with 317 of 350 MPs giving the motion the thumbs up, according to national daily El País on Tuesday.
At the summit, EU leaders will thrash out issues including putting an end to the fragmentation of Europe's financial markets, promoting youth employment and increasing the funds of the European Investment Bank made available to small and medium-sized companies.
"We wanted the proposals to reflect the real needs of the Spanish economy because of the lack of funding for SMEs, and they have done so," said Josep Sánchez Llibre of Catalonia's centre-left's CiU party, explaining his vote in favour of the resolution.
Pedro Azpiazu of the Basque National Party said: "It's important to tell Europe that we have to reorient economic policy: austerity measures alone are not enough to escape the crisis."
The cross-party deal was originally thrashed out between Prime Minister Rajoy and the leader of Spain's Socialist opposition, Alfredo Perez Rubalcaba.
Several minority parties complained of feeling snubbed after the two leaders reached an agreement last week.
No representatives of the ruling Popular Party (PP) were present in parliament on Tuesday when the minority parties discussed the resolution.
Irene Lozano of centre-left Spanish nationalist party Union, Progress and Democracy noted that German Chancellor Angela Merkel attended parliament whenever Europe was discussed while in Spain there was not a single minister present, even as a spectator, during the debate over a resolution presented as a state pact.
But she added: "It is not a state pact but a simple non-legal proposition."