European Union leaders on Thursday picked three senior politicians to head up the bloc’s institutions for the next five years, signaling commitment to Ukraine and a need for stability amid electoral upsets in Europe and, potentially, the United States.

At a summit in Brussels, the heads of the 27 E.U. member governments agreed to put forward Ursula von der Leyen, a German conservative, for a second term at the helm of the powerful European Commission, the bloc’s executive branch.

António Costa, a Socialist and until recently the prime minister of Portugal, was selected as the president of the European Council, which includes those 27 heads of government, balancing Ms. von der Leyen’s political and geographical background.

And Prime Minister Kaja Kallas of Estonia, a hawk on Russia, was the official chosen to become the bloc’s top diplomat.

The selection of these three senior politicians, who all have solid working relationships with one another, is an effort by leaders in the European Union to place relatively centrist figures at the heads of the key institutions despite the ascent of harder-right political leaders, such as Giorgia Meloni in Italy, as well as ultranationalist, nativist parties, like Marine Le Pen’s National Rally in France.

The reappointment of Ms. von der Leyen will face a serious test at the European Parliament, the bloc’s only elected institution, where she will need to lobby to earn a majority in the 720-seat assembly, in a secret ballot set to take place in mid-July. She belongs to a center-right grouping that is the largest in the Parliament, but far short of a majority.