A native of Gospić, Valentić graduated from the University of Zagreb Faculty of Law.
He was the 5th Prime Minister of Croatia from 1993 until 1995. Before being involved in politics, he was a high-ranking official of INA, the Croatian oil company. He served in that position until 4 November 1995.
A few months after taking office his cabinet de-valued the Croatian currency Croatian dinar, stopping the inflation and bringing some sort of economic stability to Croatia for the first time after the start of war.
In June 1994 the Croatian dinar was replaced with the kuna. In 1995, during his term in office, the Croatian military and police conducted Operation Storm which would ultimately lead to the end of the war in Croatia and neighbouring Bosnia and Herzegovina.
On 4 April 1993, as a member of the Croatian Democratic Union, he was appointed by President Franjo Tuđman to the post of Croatian prime minister. After his term expired, he served as a member of the Croatian Parliament until 2003.
Married; 2 children.