French President Emmanuel Macron and German Chancellor Angela Merkel hold a news conference in Berlin. “I believe in mutual trust,” Macron said. (Bernd Von Jutrczenka/AP)

On his first full day on the job, French President Emmanuel Macron appointed a former political foe as prime minister and flew to Berlin to meet with German Chancellor Angela Merkel.

Domestically and internationally, the moves were seen as attempts by Macron to build a broader base for the untested political movement that brought him to power and to affirm his commitment to restoring the historical Franco-German alliance at the heart of the European Union.

Macron’s campaign was marked by its unabashedly pro-E.U. rhetoric, and he was greeted in Berlin by throngs of supporters and a smiling Merkel, who is generally known for her stoic demeanor.

The German leader said in a news conference that the two had agreed on “the historical significance of the Franco-German relationship.” She added, “Europe can only prosper when France and Germany prosper.”

It is a tradition for French presidents to make their first official trip abroad to Germany , but Macron’s visit carried special significance.

Under his predecessor, the historically unpopular François Hollande, the vision of Germany and France as the twin engines of Europe significantly receded. This was largely because of France’s economic malaise, which has deepened in recent years.

On Monday in Berlin, Macron — who again called for a renewal of the European project — vowed to confront those domestic issues head-on. He acknowledged that high unemployment remains a problem in France and called for efforts to fight it. He also conceded that Merkel is eager for him to push through important labor and business reforms at home before major regional projects aimed at boosting Europe’s economies can be launched.

“I believe in mutual trust, and in order to reach that, everyone needs to do what they need to do,” he said. “In France, I need to apply in-depth reforms.”

A key ally for Macron in passing any liberalizing measures — a famously difficult sell in France — will be his prime minister, named Monday as Édouard Philippe.

Picking Philippe — the mayor of Le Havre, a port city in northern France — is viewed as a careful political calculation by Macron, who won the presidency without an established party structure behind him. The mix of a centrist president and a right-leaning prime minister further shakes up France’s ossified political establishment, which was uprooted in the course of the two-phase presidential election.

Macron, an independent, on May 7 became the first candidate in modern French history to win the country’s top job without belonging to the center-left or center-right parties that have run the country since 1958.

But Philippe, 46, is a member of France’s traditional conservative establishment and previously backed Alain Juppé, who was defeated in the presidential primaries last fall. Philippe earlier worked as an assistant to Juppé, a former prime minister. After Juppé’s defeat, Philippe opted to back Macron instead of his party’s candidate, François Fillon, whose campaign never recovered from a public-spending scandal.

As a prominent member of France’s center-right Republican party, Philippe could attract other conservatives to the new president’s coalition.

Macron, who was finance minister under Hollande, a Socialist, left his post last year to found his own party. His campaign sought to transcend the left-right divides with a crossover message in an age when many voters in the West have turned against globalism and establishment politicians.

To a certain extent, the political careers of Macron and Philippe share an affinity for mixed partisan affiliations. Before rallying to Juppé’s side in the early 2000s, Philippe was a member of the Socialist Party and a young devotee of Michel Rocard, a Socialist leader and former prime minister. Macron, likewise, served in the Economy Ministry in a variety of capacities during the presidency of Nicolas Sarkozy, a conservative.

As the political debate in France and elsewhere has increasingly centered on the issue of national identity in a globalized society, traditional partisan boundaries are being redrawn. In addition to conservatives such as Philippe, leftist heavyweights — such as former Paris mayor Bertrand Delanoë, a Socialist — were early supporters of Macron instead of their own parties’ candidates.

In an interview with The Washington Post before the May 7 presidential runoff, Philippe — who had previously criticized Macron — reiterated that Macron “has to implement what he promised, that is to renew the political system, the government, to mix the right and the left.”

“I will help him,” Philippe added, “because he needs help.”

As recently as January, however, he was less convinced of Macron’s potential as a leader.

In an op-ed for the newspaper Libération, Philippe wrote: “Who is Macron? For some, impressed by his power of seduction and his reformist rhetoric, he would be the natural son of Kennedy and [former far-left political leader Pierre] Mendès France. We can doubt that. The former had more charisma; the latter more principles.”

In Berlin, Macron and Merkel were slated to discuss several important issues, including Europe’s asylum system, job creation, joint European defense, and short- and medium-term measures to cut bureaucracy and reboot the E.U.

In practice, Merkel is likely to insist that Macron at least embark on domestic reforms before she agrees to the sweeping E.U. initiatives he has promoted for months. Nevertheless, on the heels of Britain’s departure from the E.U. and the rise of populists across the continent, the leaders’ meeting was seen as reassurance for Europe’s embattled political establishment.

“I for one am very aware of the responsibility at this critical point for the European Union, when we can and must take the right decision for the benefit of the people in our countries,” Merkel said.

Faiola reported from Berlin. Michael Birnbaum in Brussels contributed to this report.