West Tigers captain Robbie Farah has apologised to Prime Minister Julia Gillard for an offensive tweet he posted last year.

Farah's apology comes only days after he made a public stand against trolling on Twitter, having been the victim of such behaviour himself.

A Twitter user posted offensive comments about Farah's late mother on Sunday, which led the New South Wales State of Origin star to call for political and police intervention.

Farah asked both Ms Gillard and NSW Premier Barry O'Farrell to crack down on trolling.

But it has been revealed that Farah posted a tweet last year, responding to former rugby league international Mark Geyer, who had asked what users would buy for Ms Gillard's 50th birthday.

Farah's tweeted response was "a noose", which he later removed.

He says he has written to Ms Gillard to apologise for any hurt his post caused, highlighting the offence he took to comments made about his mother.

"As you are aware I have been vocal in recent days about criticising those who say some pretty disgraceful things through social media and I have appreciated your support in relation to that cause," the statement read.

"It is an experience that has highlighted the hurtful nature of unthinking comments and even those which are sometimes put forward as black humour.

"In the course of this I have been alerted to a tweet I made last year in relation to the Prime Minister, which was in hindsight clearly offensive.

"At the time I did think about what I had done and removed the tweet soon after posting it, but that of course doesn't repair the damage.

"I make no excuse and offer my sincere apologies.

"I can only say that I have learnt a lot in recent days and I hope that everyone in the community can learn about the pain that we can cause through such comments."

Farah says he hopes the incident "will only serve to encourage everyone to think about what we are really saying" when making comments via social media.