Pranjić started his career at Papuk. He played for NAŠK, Papuk, Belišće, and Osijek before making his move to a bigger stage at Dinamo Zagreb in 2004. While at Dinamo Zagreb, he also played regularly during their 2004–05 UEFA Cup campaign, making 6 appearances and scoring one goal in the competition.
In 2005, he was transferred to Dutch Eredivisie side Heerenveen. His good performances as an offensive winger secured him a return to international football with Croatia in 2007. He started the 2008–09 Eredivisie season well, netting four goals in his first three league matches. Pranjić scored his first hat-trick in the Dutch Cup on 12 November 2008, in a huge 7–0 win against Haaglandia. On 31 January 2009, he made the lone goal in a Heerenveen victory at Ajax. A month later, he scored a late penalty that gave Heerenveen a 3–2 win at PSV.
He won the Dutch Cup with Heerenveen at the end of the 2008–09 season, which turned out to be his last match for the club. In June 2009, Bayern Munich announced Pranjić would join the club. He struggled to make an impact in his first season with the club, starting only 14 matches and losing out to first choice left-back Holger Badstuber. However, due to his utility, and convenient injuries, he has started an increasing number of games in his second season.
Pranjić started his international career with the Croatian national under-21 football team, winning a total of 15 international caps and scoring one goal for the team between 2002 and 2004.
On 16 November 2004, he made his full international debut for Croatia in a friendly match against the Republic of Ireland. After two years of absence from the national team, he was called up for a friendly match against Norway in February 2007. Later that year, he also appeared in three UEFA Euro 2008 qualifiers.
Asked to play a defensive role by Croatia coach Slaven Bilić, although still predominantly a midfielder in his club career, Pranjić was the only Croatian to start all four games at the UEFA Euro 2008 finals. Pranjić provided an assist to Dario Srna to score the opener in Croatia's 2–1 victory over Germany and an assist to Ivan Klasnić to score the only goal in their next game, a 1–0 win over Poland.
He kept his place as a regular in the national team during their unsuccessful qualifying campaign for the 2010 FIFA World Cup, appearing in a total of 9 matches.