The candidate named by Germany's Social Democrats to challenge Chancellor Angela Merkel, Martin Schulz, has vowed to fight populism if his party wins the September election.
At an SPD party meeting in Berlin, Mr Schulz denounced eurosceptics and the "racist" rhetoric of US President Donald Trump.
The SDP has been the junior partner in Germany's grand coalition since 2013 and hopes that Mr Schulz, a former president of the European Parliament, will boost its chances of governing without Mrs Merkel's CDU.
Opinion polls suggest the Social Democrats trail the CDU, although Mr Schulz's personal rating compares favourably with that of Mrs Merkel, who plans to run for a fourth term.
In his speech on Sunday, shortly before he was formally endorsed as leader, Mr Schulz' blamed the rise of populism on a growing gap between average workers and the rich.
The 61-year-old attacked plans by Christian Democrats to cut taxes and increase defence spending at the expense of welfare programmes.
He reiterated his calls for free education, more investment such as in nursing care and schools as well as qualification programmes for the unemployed in a speech that earned him a standing ovation.
It is necessary to close the "intolerable pay gap" so men and women in both eastern and western Germany get the same amount of pay for doing the same work, Mr Schulz said.
Mr Schulz also said that as leader of the EU Parliament he had always stood up "to those who attempt to destroy this project of unity".
"Those people find in me a determined opponent," he added.
Referring to Donald Trump, he denounced what he called the president's "misogynistic, anti-democratic and racist" rhetoric.
Ahead of Sunday's convention, SPD General Secretary Katarina Barley said the party had seen 13,000 new members join this year.
Mr Schulz was the only nominee for the post of party chairman. He received 100 percent of the delegates' votes - an unprecedented result in the SPD's post-war history.
His nomination followed a decision by Germany's Foreign Minister Sigmar Gabriel to stand aside as SPD head because he thought Mr Schulz had a better chance of winning the election.
A former bookseller, Mr Schulz comes from Aachen near the Dutch border and once considered becoming a professional footballer.
- BBC / Reuters