The Government has approved plans which will allow women undergoing treatment for cancer or other serious illnesses to postpone their maternity leave by up to 52 weeks.
The legislation will ensure that those affected will not be forced to use maternity leave during treatment.
Green Party leader Roderic O'Gorman said he hoped to have the legislation in place in September, and has asked that the Bill be fast-tracked.
Speaking after a meeting of the Cabinet meeting, Mr O'Gorman said: "Maternity leave is such an important time for mothers and their babies, and so no one should be forced to use that time for undergoing medical treatment.
"The legislation approved today will mean that, where necessary, mothers will be able to postpone their maternity leave, focus on their treatment, and retain that precious time with their baby."
A campaigner had said she was hopeful the new law allowing women who are diagnosed with mental or physical illness during pregnancy to defer maternity leave can "get across the line" as quickly as possible.
According to the Irish Cancer Society, every year around 60 women go through a cancer diagnosis while pregnant or postpartum.
Under current legislation, these women are not able to defer their maternity leave when ill, so that all or almost all of their maternity leave is spent receiving cancer treatment.
Emma McGuinness, from the Irish Cancer Society's Leave our Leave campaign, was diagnosed with cancer when she was 21 weeks' pregnant, and began chemotherapy two weeks after her son was born.
Speaking on RTÉ's Morning Ireland, she said: "I then had chemotherapy every two weeks and had my maternity leave ended three days before my last chemo session."
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'A matter of equality'
Ms McGuinness said she was fortunate that her parents and family were able to step in to help her with her newborn and young daughter while she was sick and in hospital.
She added: "There were long stretches when I was in hospital with infections ... it wasn't a maternity leave, really."
Ms McGuinness explained that the piece of legislation that needs to be amended already exists in the Paternity Act, and men are able to defer their leave if they are unwell following the birth of their child.
If it exists in the Paternity Act, it should not be too much of a lift to get it changed, Ms McGuinness added.
She said: "This is a matter of equality. We are just looking to make things fair and equal.
"And it's not a malicious thing like this hasn't been left out or anything like that.
"The Paternity Act is a lot more modern than the Maternity Act, so it's just bringing it up to date.
"There's a lot of modernising to do there, but because this particular amendment exists already, we're hoping that we can just get this push through as quickly as possible."
Speaking this morning, Mr O'Gorman said the Leave our Leave campaign was to recognise that there are "women every year who undergo a serious illness during their maternity and aren't able to use that really important six months of maternity leave to be able to bond with their newborn".
He added: "They're spending that time recovering from that particular illness.
"So we're bringing forward a mechanism whereby women who have a serious illness may defer that leave for up to one year."
Mr O'Gorman was asked if women who are currently pregnant would be able to avail of the protections of the legislation, to which he replied: "We're going to write to the joint Oireachtas committee and ask for a PLS [pre-legislative scrutiny] waiver so it doesn't have to go through that process.
"So we would look to be introducing it into the Dáil and Seanad early in the next term, early in September.
"But I think we do have to wait for the legislation to pass in order to actually bestow the particular rights."
Mr O'Gorman also said that legislation would be passed on TDs availing of maternity leave.
Up until now, the matter was dealt with on an administrative basis, but this will put the process on a statutory footing.
Additional reporting Juliette Gash
