Former prime minister Jean Chrétien stands before his official portrait in Ottawa on Tuesday. (Adrian Wyld/Canadian Press)

Former prime minister Jean Chrétien, known to throw a punch or two during his time in office, has come out swinging in defence of embattled politicians at the hanging of his official portrait on Parliament Hill.

In a speech highlighting his memories of 40-plus years in Ottawa on Tuesday, Chrétien spoke of his pride in being a career politician and praised those who chose to run for public office, including his adversaries.

"We have to show respect for the men and women who devote themselves to public life," he said to a crowd that included Prime Minister Stephen Harper, Liberal Leader Michael Ignatieff, NDP Leader Jack Layton and Bloc Québécois Leader Gilles Duceppe.

"It is a very noble life," he added. "Thank you for what you are doing."

The portrait by Ottawa artist Christan Nicholson depicts an unsmiling Chrétien holding his spectacles in one hand amid a muted gold background. The 76-year-old, three-term Liberal prime minister said having his official portrait hung alongside those of the "great and not-so-great" prime ministers since Confederation is the "crowning" of his career.

He also singled out his sovereigntist rival Duceppe, noting his 20 years of public service.

"We don't agree, but he did come here to serve the people based on his convictions and his beliefs," Chrétien told the crowd. "I respect him and I respect the fact that he chose the noble career of being a politician."

Chrétien's remarks may come as comfort to MPs returning to Ottawa after hearing an earful from their constituents last week about a parliamentary board's refusal of a request by Auditor General Sheila Fraser to open the books on MPs' and senators' expenses.

Chrétien also noted that when he was young, Canada was often compared to Argentina in terms of population and geography.

However, he said, while Argentina "had a lot of military dictators," Canada was left with a bunch of "horrible politicians" who managed to oversee the peaceful change of governments and gave the best opportunities and guarantees to its citizens in the world.

"Imagine if we had been good," he joked.

Chrétien 'knew instinctively what it took to win': PM

Speaking before Chrétien, Harper began his remarks with a joke, quipping that several of his Conservative predecessors have said "the hanging of Jean Chrétien is long overdue."

Harper hailed his former rival, saying Chrétien "was and must always be remembered as a great parliamentarian" who "knew instinctively what it took to win."

"It didn't hurt that his opponents were fighting among themselves," Harper said, adding that Chrétien occasionally "appropriated" the best ideas from other parties for himself.

Harper also praised Chrétien as an unapologetic federalist and fervent defender of a united Canada. He said the unveiling of the portrait is both a tribute to a former prime minister and a testament to Canada's democratic tradition.

Chrétien also used his time at the podium to throw a few jabs at Harper, warning that in Britain in the 19th century, former prime minister William Gladstone returned for a fourth mandate at the age of 83.

"Some day you will be hung, too," he said to the prime minister, winning laughter from the crowd.

He also made a thinly veiled reference to the Conservatives' attack ads targeting Ignatieff for spending decades out of the country, saying with a smile, "Sometimes, it's good to go abroad."

Chrétien also recalled swearing in front of the Queen during the signing of the Constitution in 1982, when he realized the tip of the pen handed to him by then-prime minister Pierre Trudeau was broken.

"When I realized that, I said 'Merde' and she understood," he said. "Now I'm revealing a state secret."

With files from The Canadian Press