Michel Barnier, France’s new rightwing prime minister, has vowed to address the nation’s feelings of anger, abandonment and injustice, promising a “new era” and a break with the past. Barnier, the EU’s former Brexit negotiator, took office hours after Emmanuel Macron appointed him to form “a unifying government in the service of the country” – an attempt to put an end to two months of political paralysis after a snap election. Barnier, who at 73 is the oldest premier in the history of modern France, said his first task was to “respond as best we can to the challenges, the anger, the feeling of abandonment and injustice that is too prevalent in our cities, on our estates and in the countryside”. The government’s priority would be education, as well as security and controlling immigration, he said. “What do we expect from a prime minister?” Barnier asked. “That they tell the truth, even if it’s difficult – the truth about debt, and the truth about environmental debt, which weighs heavy on the shoulders of our children.” He said he would approach the role with “humility and determination” and promised “more action than words”. Macron shocked France by calling a snap parliamentary election in June that resulted in a hung parliament and a deeply divided political landscape. Although Marine Le Pen’s far-right National Rally came top in the first round, tactical voting saw a leftwing coalition become the biggest political force in the final round. But the left fell well short of an absolute majority of 289 seats in the national assembly. Macron later ruled out asking the left to form a government after other parties said they would immediately vote it down. Macron’s centrist faction and the far right make up the two other major groups in parliament. But Barnier’s traditional rightwing party, Les Républicains, came fourth and has only 47 seats. Barnier’s appointment was greeted with dismay by the left which will now seek to topple him with a no-confidence motion. The Socialist party leader, Olivier Faure, part of the leftwing coalition that won the highest number of seats in the election, said it was a “denial of democracy” for Macron to appoint a prime minister from the party that came fourth. “We’re entering a crisis of regime,” Faure said. Jean-Luc Mélenchon, of the leftwing party La France Insoumise (France Unbowed), said the election had been “stolen” from the French people. Controversially, Macron appears to be counting on Le Pen’s National Rally to keep Barnier in power by voting against a no-confidence motion. The RN indicated on Thursday it would not automatically vote down Barnier and would wait and see what sort of programme he laid out in his first address to parliament. Barnier was known for almost 50 years in rightwing French politics as a centrist, liberal-minded neo-Gaullist, devoted to the European cause. But in 2021, he stunned observers by significantly lurching right and hardening his stance on immigration and security as part of an unsuccessful bid to become presidential candidate for the right against Macron in 2022. Macron’s predecessor, François Hollande, said he believed Le Pen’s party had “given a kind of endorsement” to Barnier’s appointment. During a summer of political stalemate, Macron took weeks to begin to acknowledge that he had lost the snap election. His centrist party lost seats and went from its position as the largest grouping in parliament to the second grouping, behind the left alliance. After the July election deprived Macron of his relative majority in parliament, the centrist president drew out the appointment of a new prime minister for a period unprecedented since the second world war, through the July-August Olympic Games and beyond. But Macron has sought to defend his legacy and protect the reforms he had pushed through in recent years including a rise in the pension age from 62 to 64, and a hardline immigration law. Some around Macron have sought to argue that France as a whole has shifted to the right, despite the left alliance winning the biggest share of seats. Barnier served two stints as an EU commissioner and handled the thorny negotiations on Britain’s exit from the EU. He also served as a minister under the rightwing administrations of presidents Jacques Chirac and Nicolas Sarkozy. The European Commission’s president, Ursula von der Leyen, welcomed his nomination, saying she knew Barnier had “the interests of Europe and France at heart”. It remains unclear if Barnier will fully try to implement Macron’s political agenda or bring in new proposals. He will need to negotiate with other parties to get legislation adopted in parliament. Barnier replaces Gabriel Attal, who resigned on 16 July after the snap election but was kept on by Macron in a caretaker capacity. Attal, who was photographed on holiday in a T-shirt saying “I will survive”, said that eight months as prime minister was too short and that he was seeking to maintain a key role in politics. Reacting to news of Barnier’s appointment, a spokesperson for the UK prime minister, Keir Starmer, said: “We wish him all the best in his new role. The UK enjoys a strong relationship with France … We are committed to working collaboratively on shared priorities, from tackling illegal migration to supporting Ukraine.” The German chancellor, Olaf Scholz, wished Barnier “strength and every success in the tasks ahead”. He said: “Our two countries are linked in a very special way – two strong partners in the heart of Europe. I look forward to our governments continuing to work together to shape the Franco-German friendship for the benefit of our countries and Europe.” Steve Baker, the former Conservative MP who was a Brexit minister and chair of the European Research Group, told the Guardian: “I would wish him well. He is certainly going to need it as he will have his hands full dealing with the government. Michel Barnier is undoubtedly a very polished and authoritative and very consummate politician. “I am sure he will step into the role with great skill and flair, but whether that is a good thing for UK relations with the French is another thing.” The former EU chief Jean-Claude Juncker told AFP his advice would be: “My dear Michel, keep calm!”