Fathers would be able to take up to six months' paternity leave - three paid - under Government proposals to allow parents to share entitlements, it was announced today.
The new right, due to come into force from 2011, would apply during the second half of a baby's first year if the mother returned to the workplace.
But the Government conceded that take-up was likely to be low, with less than one in 16 fathers expected to leave work for a period of full-time childcare.
At present dads are entitled to two weeks' paid leave and mothers to 52, 39 of them paid.
The move was hailed by Prime Minister Gordon Brown in his speech to the TUC in Liverpool.
"No Tory government has ever given a single day of paternity leave. This Labour government gave men the right to two weeks' paternity leave," he told trade unionists.
"Now, from April 2011, we will give fathers the right to take up to three months' additional paid paternity leave during the second six months of a child's life, if the mother has returned to work, because Labour believes in giving couples more freedom, dads more rights and children more time with the two people who love them most."
Extended paternity rights were promised in Labour's 2005 general election manifesto alongside a "goal" to extend paid maternity leave to a full year.
Mr Brown said Labour "retain our ambition" to that move although it was not included in today's proposals, which will now go out to consultation.
Business Minister Pat McFadden said the impact on businesses would be small, affecting less than 1 per cent of small firms.
"We will work with business to make sure any changes are introduced in a way that minimises burdens and gives them predictability in the provision of leave," he said.
"As family-friendly policies have been introduced we have seen more retention of mothers in their current jobs when they go back to work."
Harriet Harman, Minister for Women and Equality, said: "This gives families radically more choice and flexibility in how they balance work and care of children, and enables fathers to play a bigger part in bringing up their children."
The rights will apply to parents of children due on or after April 3, 2011. Estimated take-up is less than 6 per cent.