Jean-Marc Ayrault, a former German teacher who has been working behind the scenes to smooth Paris's relations with Berlin, has been appointed prime minister by the new French president François Hollande.

Ayrault, 62, an MP and mayor of the north-western city of Nantes, has been the vocal leader of the Socialist parliamentary group for 15 years and is seen as a "normal" prime minister for a "normal" president, fitting Hollande's promised pared-down style at the top of French politics.

An adviser to Hollande throughout the presidential election campaign he has carried out sensitive missions as one of the key Germany experts around Hollande. Last year, he met advisers to Angela Merkel in Berlin in an effort to build ties with her conservative government before Hollande, now France's first leftwing president in nearly 20 years, began his quest to temper Europe's austerity drive with growth measures.

Once known for holidaying in a 1988 Volkswagen Combi camper van, Ayrault is seen as a pragmatist and consensus-politician in the same mould as Hollande. Both are local politicians with strong regional roots. Ayrault, who has been mayor of Nantes for more than 20 years, hasn't lost an election since 1976 and is an expert in the workings of parliamentary politics. This will be crucial if he is to lead the Socialist party's fight for a much-needed majority in the assembly elections next month, without which Hollande would have difficulty enacting his manifesto pledges.

The son of a factory worker, Ayrault is a former teacher from western France. He comes from a very different background to many of Hollande's top allies who went to the Ecole Nationale d'Administration, or ENA, France's elite graduate school for civil servants.

In his youth, he was initially on the Socialists' leftwing before shifting towards a firm social-democrat stance on the centre of the party, matching that of Hollande.

For 15 years, Ayrault and Hollande sat next to each other on the benches of the French parliament and are known to trust each other. Hollande had said during the campaign that it was important to govern with someone he gets on with. But Ayrault, like Hollande has no ministerial experience and has never served in government.

Ayrault's appointment as prime minister had been expected for weeks. But it was uncertain whether he would be affected by complaints from rightwing opponents that he had received a six-month suspended prison sentence in 1997 and a fine worth roughly €4,500 for a printing contract for a local newspaper that was awarded without a public tender.

Hollande had said during the campaign that he would not put anyone with criminal convictions in his cabinet. Ayrault had hit back saying he had taken responsibility for the affair as mayor, but his personal integrity had not been questioned.

"It was 15 years ago. I have never hidden anything, especially not to the people of Nantes who re-elected me twice. It's an affair which did not involve me personally but which I took responsibility for as mayor," he posted on his Facebook page. "There was never any question of personal enrichment or political financing. I am an honest man and I will remain an honest man."

A classical music and arts fan – Le Monde reported he likes modern dance and can tango – Ayrault is said to have boosted Nantes's standing on the cultural festival circuit. But the Socialists recently moved to calm controversy and high-profile protests over a new airport project near Nantes which Ayrault had supported.

The rest of the government, which Hollande has promised will feature as many women as men, is due to be announced on Wednesday.