In 1990 Biškupić joined the Croatian Democratic Union party (HDZ) and in 1992 was appointed assistant to the Minister of Culture. From 1993 to 1995 he served as Deputy Mayor of Zagreb. From November 1995 to January 2000 he served his first term as Minister of Culture, under Prime Minister Zlatko Mateša. After his term ended he ran in the parliamentary elections and was elected to the Croatian parliament three times at the 2000, 2003 and 2007 elections. He was appointed Minister of Culture again in December 2003, under Prime Minister Ivo Sanader, and was confirmed to serve a second term in January 2008 after HDZ won the 2007 elections again.