Europe’s largest political group, the centre-right European People’s party, has chosen the long-serving German MEP Manfred Weber as its candidate to lead the European commission – one of the top jobs in the EU.

Weber, who was backed by the German chancellor, Angela Merkel, is the favourite to lead the commission, the powerful executive that drafts and enforces EU law, but he exceeded expectations, capturing 80% of 619 party delegate votes.

A soft-spoken Bavarian who has spent most of his career in politics, Weber leads the EPP in the European parliament, but is little known in his home country. He once described European values as “inspired by our Christian roots”, and ran a campaign stressing his love for his home village.

He defeated Alexander Stubb, a multilingual former Finnish prime minister who attended the London School of Economics.

Weber’s strong victory puts him in pole position to succeed the current commission president, Jean-Claude Juncker, if the EPP wins the largest number of MEPs in European elections in May.

The winner was elected after a two-day conference in Helsinki that featured a warning from the EU’s chief Brexit negotiator, Michel Barnier, that the bloc was threatened by “a [Nigel] Farage in every country”.

The parliament’s second-largest political bloc, the Socialists and Democrats, this week chose the current European commission vice-president, Frans Timmermans, as its lead candidate for the job.

The EPP vote came amid tension within the group over how to manage Hungary’s increasingly authoritarian prime minister, Viktor Orbán, who has caused alarm with charged nationalist rhetoric and laws targeted at NGOs.

Hungary’s prime minister, Viktor Orbán, has caused concern in the EU with his domestic policies and rhetoric. Photograph: Bernadett Szabó/Reuters

Challenged on Orbán, Weber promised that as commission president, he would propose “binding rule-of-law legislation” in order to tackle backsliding on fundamental democratic values in any EU member state.

He did not spell out how his plan would work, or whether it would be stronger than the existing lengthy process known as article seven, which relies on peer pressure by other EU members.

The EU has opened a rule of law investigation into Poland and Hungary, but so far, results are not clear. “On the concrete details of the rule of law mechanism, give us a chance to work on this,” Weber said, while insisting the EPP would not compromise on its values.

Following his victory, Weber recalled that he voted to launch an EU sanctions procedure against Hungary. “The EPP doesn’t need any kind of lesson from anybody,” he said, pointing to concerns over corruption in Romania’s socialist government.

The German MEP could soon be tested again, as the EPP is said to have received membership applications from Poland’s nationalist Law and Justice party, as well as the rightwing populist League in Italy. Asked whether such parties could join to bolster EPP numbers, Weber said as group leader he had managed to keep “the right extremists” out of powerful jobs in the European parliament.

“I draw a very clear red line to the real Nazis inside the European parliament; unfortunately, they are there,” he said, adding that the EPP had even voted for a communist to become one of the parliament’s 14 vice-presidents, “because we think they have to be included, but we never vote for any kind of right extremists”.

Stubb argued Orbán should leave the EPP if he does not sign up to a European statement of values agreed upon by EPP delegates on Wednesday.

The guidance states that the bloc’s money should not be spent in countries “where fundamental EU values and the rule of law are not respected”, or where there is no cooperation with investigations by the EU’s anti-fraud office – an implicit reference to Orbán, who has been accused of treating the EU like a cash register.

The EPP hierarchy opposes throwing Orbán out, fearing that could boost the nationalist right. “In every family there is an enfant terrible,” said Joseph Daul, the EPP president. “But as I am a Christian Democrat, I prefer keeping my enfant terrible inside the family and to try to talk to him, to reason with him.”

Jean-Claude Juncker, the current European commission president, at the European People’s party congress. Photograph: Kimmo Brandt/EPA

The European council president, Donald Tusk, who is disliked by anti-EU populists in his native Poland, offered a veiled rebuke to Orbán. Standing on the podium metres away from him, Tusk said: “If you don’t like the free press and NGOs, if you tolerate xenophobia, homophobia, nationalism and antisemitism, you are not a Christian Democrat.”

In his speech, Orbán was uncompromising on what he saw as failed policies. “We have to take the responsibility for not being able to keep the British in and the migrants out,” he said.

Weber will also face questions about whether the candidate of the largest political group should automatically take charge of the commission, once the election results are clear.

EU leaders dislike the system and have insisted there is no instant link that means the lead candidate of the biggest group after the elections is propelled to the top job. Proponents argue it is more democratic, because the electorate of nearly 450 million gets to choose. “The key question now is what the people think,” Weber said. “No one in the European council [of EU leaders] can say I don’t care.”

That argument has been rejected by national governments. “It is bullshit,” said one senior European source, arguing there was nothing undemocratic about democratically elected governments choosing people to run the EU’s institutions.

In 2014, government leaders had little choice. Luuk van Middelaar, who was a senior adviser to the European council president at the time, recalled: “They felt cornered. They didn’t like the system, but they had to swallow the nomination of Juncker. Even the Bild newspaper was writing that the EU would look like a banana republic if it didn’t nominate Juncker.”