The right-wing Spanish leader, 62, is looking to pick up support within the bloc as the country hosts an EU summit for the first time in years, which will tackle the issue of Brexit amongst the southern European countries.
Leaders of France, Italy, Portugal, Greece, Cyprus and Malta – along with Spain – will gather at the El Pardo palace outside Madrid later today.
A statement issued by the office for Mr Rajoy said the meeting was a chance to "launch a message of unity and commitment to the project of European integration at a decisive moment in our history”.
Spanish Prime Minister Mariano Rajoy (L) is expected to push for support over Gibraltar
It continued: "Europe must continue to work to address the issues of greatest concern to its citizens and strengthen its project of integration.”
Officially, the meeting has been arranged for the countries involved to agree a common position of the southern EU countries regarding Brexit and the future direction of the bloc.
However, Mr Rajoy is expected to use the gathering as a chance to push his view that Gibraltar should return to Spanish ownership.
Spanish Prime Minister Mariano Rajoy
Borja Lasheras, director of the Madrid office of the European Council on Foreign Relations said: “There is a real willingness in Spain to regain influence at a time when other top European countries are absorbed by their own problems.
“Spain is playing its cards, and other countries are not.”
Also on today’s summit agenda is the issue of immigration, of particular interest to southern EU states which are on the frontline of the problem
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The leaders will also discuss economic, social and defence policies as well as the crisis in Syria, according to a French diplomatic source.
The meeting of the leaders will be the third by the group following gatherings in Athens in September and Lisbon in January.
Spain has been emboldened in its position on the world stage after the EU published its Brexit negotiation guidelines.
The question of Gibraltar is expected to be raised at a meeting of the southern EU countries
After some last-minute negotiations from Mr Rajoy, the text included a reference to Gibraltar.
Any post-Brexit agreement between the UK and the EU would not apply to Gibraltar “without the agreement between… Spain and the United Kingdom”, the statement said.
It indicated, at least in diplomatic terms, the EU was siding with Spain over the issue of the territory on The Rock.
Spanish Prime Minister, Mariano Rajoy (L), greets his Cypriot counterpart, Nicos Anastasiadis (L)
Salvador Laudes, a foreign policy analyst at the Real Instituto Elcano think tank in Madrid said: “Spain lost influence in recent years, in part because of the economic crisis at home and in part because of the EU’s expansion.
“But since the formation of the [second Rajoy] government last year there is a clear sense that Spain wants to return to a more constructive and ambitious spirit in Europe.”
Spain will also be following the developments over the question of Scottish independence as it tries to suppress its own independence battle with Catalonia.