Former prime minister Jean Chrétien is reopening the debate on a Liberal-NDP merger, arguing that a merger turned out well for the Conservatives.

Speaking in an exclusive interview with Evan Solomon, host of CBC's Power & Politics, Chrétien said the merger will happen soon or not at all.

"It will be done one day. It will come very quickly or not happen. Look at the way that Harper did that — Harper had MacKay there. [He] made a solemn promise in writing that never he will talk merging with the Reform [Party]. He's now the minister of defence. Things happen and they happen, sometimes, at moments unexpected."

In 2003, the Progressive Conservatives, led by Peter MacKay, merged with now-Prime Minister Stephen Harper's Canadian Alliance. The Reform Party was the forerunner to the Canadian Alliance.

Chrétien says the Liberals talked about merging with the CCF, the predecessors to the NDP, in 1956.

"If they had done it ... a lot of people think, and I think too, they would have been the government today."

Liberal and NDP officials have denied rumours that Chrétien and NDP stalwarts Ed Broadbent and Roy Romanow chatted occasionally about the possibility of the two parties merging. Broadbent, the former NDP leader, says he doesn't support a merger between the NDP and Liberals.

NDP MP Pat Martin has said he'll run as the pro-merger candidate to replace Jack Layton, the late NDP leader, if no other candidate is open to the option. Martin says he thinks it's something the party should consider.