Mr Blackburn, 58, will be replaced by James Crosby, 42, the group's financial services and insurance director. Mr Blackburn will stay on as vice-chairman, a non-executive post, until December next year.
The announcement came as a surprise to the City, which had been expecting Mr Blackburn to remain chief executive until December 1999, when he will retire. Halifax said its board had decided the question of his succession should be resolved "well in advance of his actual retirement".
Halifax's share price jumped from 765p to 780p on the news. Analysts said Mr Blackburn had been under some pressure because of the difficulty the bank was having in rebuilding its share of the mortgage market.
Mr Blackburn has also been under fire from some analysts over the bank's pounds 750m bid for Birmingham Midshires. The takeover, to be approved by Midshires' members in December, is perceived as an expensive buy that will bring little value to Halifax.
But Mr Blackburn said there was no need to change direction. "In strategic terms nothing has changed since [chairman] Jon Foulds and I were marketing the company in May 1997. The strategy is still to balance our income stream so that 50 per cent of it is coming from our core business," he said.
Mr Blackburn, who has piloted a merger with Leeds Building Society followed by a flotation of the combined group, said he was fulfilling a long-cherished desire to spend more time with sons from his second marriage, aged 7 and 10.
"I'm very anxious to be a two-parent family again. I could always see that come my late 50s, there would be things I would have to accept in taking on a different rhythm and pace to my life. But equally I have had all sorts of approaches in a non-executive capacity, which I have had to say no to."
Asked about the timing of his departure, Mr Blackburn said it would give Mr Crosby the chance to take the group forward from the start of the company's year.
The appointment of Mr Crosby will fuel speculation that Halifax is planning further acquisitions in life insurance. The Halifax has about pounds 3bn to spend on acquisitions.
Outlook, page 21Reuse content