Jeremy Corbyn has diverted from his usual campaign stump speech to deliver a rare retelling of his personal history, his motivations and his views on leadership.

The speech at his former university in London recalled the election tactics of the former Labour leader Neil Kinnock and former Conservative prime minister John Major, who released video biographies in an attempt to woo voters. Taking questions from the press and audience afterwards, Corbyn denied the speech was a rebranding exercise and insisted it was a one-off.

“As you know, I am very averse to talking about myself and that has been the story of my life … I am not going to spend the whole election campaign talking about myself any more, so you had the chance today,” he said.

Labour strategists are keen to contrast what they portray as a cold Conservative prime minister with what they see as Corbyn’s warmer personality. They are also anxious to contrast his willingness to take questions from the media with what they claim is Theresa May’s avoidance of scrutiny.

Speaking at the London Metropolitan University in front of about 200 people, most of them Labour supporters, he began: “This morning I’m going to say a few words about you, and even some about me.”

After lengthy passages about the Conservatives’ impact on living standards, he said: “And now for a sentence I’ve yet to utter in my political life. Enough about you, what about me?”

Throughout his 34 years as an MP, he had been attacked for what he believed in, he said, but it had not changed his core values.

Many of the problems he identified at the start his career were still present. “In 1983, I stood up in parliament for the first time and used my maiden speech to condemn deeply damaging cuts in public services and the NHS. It’s a tragedy that I could make a very similar speech today and it would once again hold true.”

He said he believed being an MP could bring profound and lasting change and recalled his early days as a parliamentarian. “At the time, young protesters were being shot dead on the streets by the racist apartheid regime in South Africa. Nelson Mandela and hundreds of ANC leaders were in prison. The Conservative government refused to impose sanctions, entertained the leaders of the regime and banned protests outside the South African embassy in London,” he said.

“Being an MP helped bring attention to that ban and the wider cause of South Africa’s liberation, and got a group of us arrested. But the space for people in Britain to organise in support of freedom in South Africa was defended and strengthened. And I realised then that political leaders can, if they want to, create and preserve the space for others to organise and transform countries.”

His yardstick for measuring the performance of Labour and Conservative governments over the last three decades was the extent to which they dealt with unfairness and created a better society, he said.

“In that time, I’ve seen prime ministers and leaders of the opposition come and go, but for all their achievements and failures, what I didn’t see was a sustained attempt to rid this country of what really holds people back. I never heard a clear invitation for everyone in the country to work together and create a real alternative to our rigged economy,” he said.

“So when I was asked to put my name forward in Labour’s 2015 leadership election, I felt I should step up.”

As leader he said he had forced the government into U-turns on tax credits, disability payments and attempts to increase national insurance for the self-employed.

On his leadership philosophy, he said his critics had a right to make a reasoned case and challenge him. If leaders go unchallenged, they can make some of the most damaging mistakes, he said. ”And if party leaders put themselves ahead of serving the people, they stop listening and even put our country at risk.”

He said there were signs the prime minister and her closest advisers were slipping into a presidential bunker mentality. “Whereas it is the job of leadership to hold open the space for dissent, new thinking and fit-for-purpose policy,” he said.

“Whereas insecure leaders want to feel stronger by asking you to give them more power, I recognise strong leadership as equipping you with more power.”

He said he would not allow free thinking to be “shut down by a hostile media or an elite that scoffs at anyone who dares to step out of line”.

He used the speech to make a plea for 2.4 million young people missing from the UK’s electoral register to sign up. He said barely 40% of 18 to 24-year olds turn out to vote.

“The Conservatives are more than happy with this state of affairs. Apathy and resignation will secure them seats on election day,” he said.