One of nine children of a small farming family, he was born in 1949 in Lispole, part of the Dingle Gaeltacht in County Kerry. He went to school in the Dingle Christian Brothers School, and after finishing he enrolled in the priesthood. As part of his training he was sent to a Catholic seminary school in Minnesota, United States in the 1960s.

It was against the backdrop of anti-Vietnam War protests and the civil rights movement, that Higgins was politicised. He is a brother of Liam Higgins, who played football with the Kerry GAA senior team in the 1960s and 1970s.

Higgins returned to Ireland and attended University College Dublin, studying English and French. For several years he was a Teacher in several Dublin inner city schools. While at university he joined the Labour Party and became active in the Militant Tendency, an entryist Trotskyist group that operated within the Labour Party. Throughout his time in the Labour Party he was a strong opponent of coalition politics along with TDs Emmet Stagg and Michael D. Higgins. He was elected to the Administrative Council of the Labour Party by the membership in the 1980s. In 1989, Higgins was expelled alongside 13 other members of Militant Tendency, by party leader Dick Spring. The group eventually left the party and formed Militant Labour, which became the Socialist Party in 1996.

Higgins spends over half his salary on the Socialist Party and causes he supports. Higgins was elected to Dublin County Council in 1991 for the Mulhuddart electoral area and was until 2003 a member of Fingal County Council. In 1996, he campaigned against local authority water and refuse charges and contested the Dublin West by-election, losing narrowly to Brian Lenihan, Jnr.

Higgins was first elected to the Dáil at the 1997 general election and re-elected at the 2002 general election. He lost his seat at the 2007 general election, but regained it at the 2011 general election. From 2002 to 2007, he was a member of the Technical Group in the Dáil which consisted of various Independent TDs, Sinn Féin and the Green Party grouped together for better speaking time.

On 19 September 2003, Higgins was sentenced to one month in Mountjoy Prison as a result of his protest against the non-collection of refuse in his constituency during the Anti-Bin Tax Campaign. He was also prominent in the successful 2005 campaign to bring Nigerian school student Olukunle Eluhanla back to Ireland after he had been deported. Higgins remains an opponent of the deportation policy.

At the 2004 European Parliament election, Higgins received 23,200 (5.5%) votes in the Dublin constituency, double his 1999 result, but did not win a seat.

Higgins used his platform in the Dáil to raise the issue of exploitation of migrant and guest workers in Ireland. He and others claimed that many companies were paying migrants below the minimum wage and, in some cases, not paying overtime rates. In March 2005, Higgins and a delegation of Turkish ex-employees of GAMA Endustri, a Turkish construction firm working in Ireland, travelled to Amsterdam, Netherlands, where they discovered that GAMA had been secreting up to €30 million in workers' wages without their knowledge. He expressed opposition in the Dáil to the jailing of the Rossport Five in July 2005. He raised the outsourcing of jobs by Irish Ferries in the Dáil in November 2005, requesting new legislation to regulate what he described as "these modern slavers".

In October 2006, Higgins requested the suspension of normal Business in the Dáil after it emerged that Ryanair had upped its share in Aer Lingus overnight, amid concerns for workers' rights and Passenger welfare.

In 2008, Higgins was a political opponent of the Irish government's first Treaty of Lisbon referendum. He described the success of the "No" campaign as "a huge rebuff to the Irish political establishment".

In 2009, Higgins was a political opponent of the Irish government's re-run of the Treaty of Lisbon referendum. He said the guarantees did not change the Treaty. Higgins said, "The overall agenda here is quite simply the ruling classes, or the classes of Europe intend to stride on to the world stage as a powerful economic entity. And they want to be as powerful as the US, meaning they want a stronger foreign policy and a military wing to back them up." He also spoke out against Ireland's Catholic bishops, who claimed neither a "Yes" nor a "No" vote would threaten the unborn, saying that EU spending on arms ought to be enough for the bishops to join the "No" campaign.

On 23 November 2010, Higgins walked out of a meeting of Irish MEPs with EU Economic and Monetary Affairs Commissioner Olli Rehn, after two minutes in Strasbourg, prompting criticism from Fine Gael MEP Gay Mitchell. Higgins said he walked out as information Rehn was giving was to be confidential and that he felt it would have been a betrayal to stay, calling it "unacceptable".

In the Dáil, Higgins accused Tánaiste Eamon Gilmore of doing nothing for the 14 Irish citizens being held "incommunicado" by Israel in November 2011. In December 2011, Higgins described as a disgraceful campaign of intimidation the fines imposed by the government on people who were unable to pay a new household charge brought in as part of the latest austerity budget and said to Enda Kenny that he would be "the new Captain Boycott of austerity in this country". He asked that Minister for Finance Michael Noonan provide EBS staff with the 13th month end of year payment they were being denied.

In September 2012, he publicly disagreed with former Socialist Party colleague Clare Daly, saying it was "unfortunate" that she had resigned from the party, but that it was impossible for Daly under the banner of the Socialist Party to continue to offer political support to Mick Wallace, who was at that time embroiled in scandal.

In April 2014, he announced he would not contest the next general election the Dáil, though he would remain in politics in a different capacity. At the time he stated his belief that the “baton of elected representation” should be carried by another generation of Socialist Party politicians — like Ruth Coppinger and Paul Murphy. To this effect, Higgins assisted Cian Prendiville with his Seanad nomination.