Fine Gael TD Tom Barry has been "severely reprimanded" by the party's general secretary after an incident during the Dáil debate on the Protection of Life During Pregnancy Bill.
The Cork TD was seen pulling a female colleague onto his lap during the debate.
The incident, which occurred at around 2.40am was caught on camera while TDs were gathering for the first vote on the bill.
In a statement Mr Barry said: "What I did was disrespectful and inappropriate. I have apologised to Áine Collins and she graciously and immediately accepted my apology.
"No excuses, I just shouldn't have done it."
A statement from Fine Gael said the party does not regard the incident as mere horseplay, adding that it was all the more inappropriate given where it took place.
Fine Gael General Secretary Tom Curran said: "I wish to make it clear that the instinctive characterisation of the incident as 'horseplay involving two people' doesn't reflect how Fine Gael views this kind of behaviour, having seen the footage."
It is understood Tom Barry was severely reprimanded in a meeting with the general secretary.
Mr Curran said Mr Barry's apology makes it clear he understands the inappropriateness of his actions.
"We welcome his apology and the fact that Deputy Collins has accepted it," he added.
A Fine Gael spokesperson earlier said the incident was "silly" and "shouldn't have happened", but that there was "no malice involved."
The National Women's Council of Ireland described the Dáil and Irish politics as a woman-unfriendly place following the incident.
Speaking on RTÉ's News at One, NWCI spokesman Eoin Murray said it was up to Ms Collins to decide how she wanted to respond to the incident.
Mr Murray said that gender quotas would not be a solution to all of the problems.
Standards of behaviour should be at their very highest in the Dáil and be the same as every workplace in Ireland, he added.
Mr Murray urged parties to make sure that political chambers were free from sexist behaviour to make sure that politics is a welcoming place.
Taoiseach Enda Kenny said he had not seen the incident.
Asked if he would watch the footage, Mr Kenny said he was interested in people being able to contribute to a serious bill in respect of the lives of women and the lives of their unborn children.
Minister for Jobs Richard Bruton said: "Obviously this was a very important debate and I don't think we want to get side tracked by an inappropriate incident."
Minister for Children Frances Fitzgerald said: "Last night was a very important debate on critical issues, everyone around the house contributed to it, let's not be distracted from that important debate by an inappropriate incident."