George Lee has resigned from the Dáil and from Fine Gael, just nine months after his election.
He said the decision had been difficult, but that despite his best efforts, he had had virtually no influence on shaping Fine Gael's economic policies.
Mr Lee was elected in the Dublin South by-election last June.
Speaking on RTÉ News At One, George Lee said he had wanted to play a part in forming Fine Gael economic policy.
'For the last nine months I've done my best to have an influence on that, but I have to confess that I have virtually no influence no input whatsoever.'
'I was appointed chairman of an economic forum without my consultation whatsoever - which wasn't the role at all which I wanted to play.'
Asked why he did not secure the role he wanted within Fine Gael, he said he had been talking to Fine Gael leader Enda Kenny in the past week.
'And although a role may well have been provided I believe from my point of view it is too late. Nine months is a long time.' he added.
He thanked everyone who helped him but says he would not be serving the electorate honestly if he were to continue in office.
Mr Lee rejected the suggestion that he had found it difficult to adjust to the demands of the job, and said that senior people in Fine Gael and its front bench 'did not look for my advice on anything'.
Insisting that it was nothing to do with being on the front bench, he said he did not know if he had been cold shouldered, 'all I know is that I wasn't involved.'
'I don't know 100% what I am going to do now ... I think I will be probably going back to RTÉ.'
RTÉ has confirmed that Mr Lee is on a year's unpaid leave of absence, which expires at the beginning of May.
In a statement this evening RTÉ said: 'RTÉ has not yet heard from George Lee with regard to his intentions at the end of the period of leave of absence.
'The normal situation is that a member of staff on leave of absence is assured of employment within RTÉ on their return, but not necessarily to the position which they left.'
Taoiseach Brian Cowen said he was surprised at Mr Lee's decision.
He said it is a big decision, he wished him well and he said politics is a tough life and a tough career.