McGrath was educated at St. Joseph's College, Cahir; Kildalton Agricultural College, County Kilkenny and University College Cork. He was a member of South Tipperary County Council from 1999 to 2007, and served as chairperson of the council from 2004 to 2005. McGrath was found not guilty of assault of a teenager in south Tipperary following a trial in 2008. McGrath made a complaint to the Garda Ombudsman's office in relation to the handling of the investigation. In October 2009, McGrath criticised the proposal by Noel Dempsey to lower the legal level of alcohol in drivers, claiming that for some people a small amount of alcohol made them less nervous behind the wheel, though he said he didn't condone drunk driving. His comments were criticised by Road Safety Authority chairman Gay Byrne and the Automobile Association. In June 2010, McGrath accused Minister for the Environment, Heritage and Local GovernmentJohn Gormley of the Green Party of bullying Fianna Fáil over the bill to ban stag hunting, which was passed in the Dáil on 29 June 2010. Gormley said the bill was a part of the renewed programme for government and that it was a relatively minor piece of legislation, which should not have taken up so much Dáil time. McGrath voted against the bill and lost the Fianna Fáil parliamentary party whip as a result. He explained he was independent minded and would not be silenced by anybody. He further qualified his support for the government in September 2010. On 25 January 2011, McGrath announced that he was leaving the Fianna Fáil party and would contest the 2011 general election as an independent candidate. He denied that he was cynically resigning from the party in an attempt to save his own Dáil seat, saying that he had run out of “final straws” with Fianna Fáil. He also said that widespread unemployment, pay cuts, negative equity, the recent price hike at health insurer VHI and the recent leadership debacle had forced his hand. At the election on 25 February, McGrath secured his seat on the fifth count, having polled 14.7 per cent of the first preferences, defeating a challenge from Labour's Senator Phil Prendergast. He is a member of the Rural Independents Technical group in the Dáil. McGrath is opposed to same-sex marriage, and was the only TD to speak against it in the Irish same-sex marriage referendum when it was debated in the Dáil. He said he would “probably” vote No in the referendum to allow same sex couples to marry in 2015. McGrath is a pro-life advocate. He supported the "No" side in the 2018 abortion referendum. In November 2018 he supported amendments to the Regulation of Termination of Pregnancy Bill which would require pain relief to the foetus during termination, which were subsequently defeated.
