Bishop Haľko was born in Bratislava, Slovakia, on 10 May 1964. From 1986 to 1990 he worked as a lecturer for vocational education in the Institution for Welfare in Bratislava, then as a worker in the Bratislava Water and Sewerage Company. He also completed the two years of national service. He was ordained as a priest in Trnava on 4 July 1994. In 1997 he was assigned to the pastoral care of Hungarian believers.
From 1997 to 2011 he taught Church History at the Theological Faculty of Comenius University (CMBF) in Bratislava, serving as lecturer in Church History at the same Faculty from 2006. In 2008–2011 he was a member of the College of Consultors of the Archdiocese of Bratislava, a member of the Council of Priests, Director of the media centre and spokesman for the Metropolitan Archbishop. In 2009 he was appointed by Pope Benedict XVI as chaplain to His Holiness.
He was named as Auxiliary Bishop of Bratislava on 31 January 2012. His Episcopal consecration took place on 17 March 2012.
In November 2012, Mgr. Haľko was appointed by the Slovak Bishops’ Conference as its COMECE Bishop Delegate.
Since March 2023, he is the President of the COMECE Commission on Migration and Asylum.