The Conservatives have called for more flexible parental leave, arguing parents should be able to share time-off.
Under the Conservatives' proposals, new mothers and fathers would be able to take up to six months off work simultaneously, or divide a year's parental leave between them.
David Cameron argued this would be good for families as well as helping to close the gender pay gap by undermining the assumption that it is always women that will take a lengthy career break if they choose to have a child.
The Fawcett Society has welcomed the proposals but Labour has claimed they would be impractical for many families.
By 2010 the government plans to extend parental leave to 52 weeks, with the mother required to take the first 26 weeks.
But Mr Cameron argued there was no reason why parents should not be able to decide between themselves who should go back to work.
"Let's make it completely flexible," he told GMTV.
"So if mum and dad want to take time off together at the beginning let them do that.don't say that the woman has to take 26 weeks."
The Conservatives still say the mother should take the first 14 weeks of leave to help her bond with her baby, but Mr Cameron said parents should be able to split the remaining 38 weeks.
This could enable both parents to stay at home for 26 weeks.
The Tory leader said the proposal was about "making Britain more family-friendly and helping couples stay together".
He also argued it would help to tackle the gender pay gap.
"Women are not getting into some of the jobs that are higher paid because they are the ones who are expected to take all the leave when the baby comes," Mr Cameron explained.
Katherine Rake, director of the Fawcett Society said shared parenting was a "crucial step" towards tackling the root causes of gender inequality.
"Flexible parental leave would enable mothers and fathers to strike the balance they choose between caring and employment," she said.
The proposal marks a shift in policy for the Conservatives and business secretary John Hutton pointed out Mr Cameron had opposed previous attempts to extend parental rights.
He argued that for most families it would be financially unrealistic for both families to stay at home.
"So the Tory big idea on the family shows how out of touch they are with hardworking people," Mr Hutton continued.
"In reality very few families would be able to take advantage of offering paternity leave to both parents at the same time because this implies a major drop in family income at the critical moment in a new born baby's life."
The Office for National Statistics says average male income is now £498 a week, compared to statutory maternity leave of £112.75.