Viduka captained the Australia national team at the 2006 FIFA World Cup, reaching the Round of 16, which remains their joint-best performance to date.

In the same month as his signing, Celtic announced that Viduka had quit the club without kicking a ball for them, citing stress as his reason.

These issues were eventually resolved and Viduka made his first appearance in a Celtic shirt on 16 February 1999, scoring for the under-21 team as an over-age player in a 4–2 victory against Motherwell.

After making his first team debut against Dundee United on 27 February 1999,[11] his first goals for the club came when he scored a brace against Greenock Morton in the Scottish Cup on 8 March 1999.

[13] In February 2000, lower league team Inverness Caledonian Thistle defeated Celtic in a shock upset in the third round of the Scottish Cup.

At Leeds, he was expected to line up in a three-pronged attack alongside the previous season's top scorer Michael Bridges and Australia teammate Harry Kewell, but injuries to those two saw him form a partnership with Alan Smith in Leeds' Champions League matches, while Robbie Keane – signed on loan from Inter Milan as cover for Bridges – also benefited in their Premier League matches together in the second half of the season.

[15] In the 2002–03 campaign, Viduka scored another 22 goals, including a hat-trick in a 6–1 win at Charlton Athletic[16] and the winner in a 3–2 victory at Arsenal on the penultimate day of the season that effectively saved United from relegation.

However, the club's financial crisis continued, and resulted in the sale of key players including Harry Kewell and Robbie Keane.

The squad was bolstered with a number of high-profile signings to cope with the increased fixture list and to ensure it could compete on the European stage.

With his contract due to expire at the end of the 2006–07 season, Middlesbrough manager Gareth Southgate expressed his interest in retaining Viduka.

Given his impressive haul for the season, Viduka attracted interest from a number of clubs who were hoping to sign him on a free transfer as he became out-of-contract.

After an injury lay off over the new year, Viduka was brought back into the side by new manager Kevin Keegan, where he played as part of a 4–3–3 formation along with Michael Owen and Obafemi Martins.

Viduka made his return to the first team after six months out injured at former club Middlesbrough, coming on for Martins as a substitute on 29 November 2008.

This was a great relief for manager Joe Kinnear, who stated that he had previously feared the Australian's career might have been prematurely ended by his injury woes.

Viduka, however, later expressed his desire to continue playing past this season after acquiring a groin injury in late December.

[24] After returning from injury, he was immediately used by newly appointed coach Alan Shearer in an attempt to prevent the team's relegation.

After playing a man of the match performance in the 3–1 victory against his former team Middlesbrough, Mark appeared to have scored his first goal of the season against Fulham.

Match referee Howard Webb, however, ruled that Kevin Nolan impeded goalkeeper Mark Schwarzer disallowing the goal.

Kewell scuffed his shot but the ball bounced kindly to Mark Bresciano who went on to score the goal that forced the Qualifier to go to a penalty shoot out.

[42] Viduka also led Australia's national team to their first World Cup finals victory with a 3–1 win over Japan in June 2006, as well as guiding them through an encounter with Brazil, losing 2–0, and a controversial bout with Croatia, ending with a 2–2 draw.

Although a regular scorer in the Premier League, Viduka has struggled to score any significant goals for the Socceroos, and the 2006 World Cup was no different.

Viduka considered retiring from international competition after the 2006 World Cup, citing increasing family commitments as the primary reason.

On Australia's first ever Asian Cup participation, Viduka captained the side and he scored their solitary goal against Iraq, a game which they ultimately lost 1–3.

He missed World Cup Qualifiers against Qatar, Bahrain and Japan, even though fully fit and asked to play by then-Socceroos manager Pim Verbeek.

[48] His father Joe immigrated to Australia from Croatia in the 1960s, and Croatian footballer and Ballon d'Or winner Luka Modrić is his cousin.

[52] Middlesbrough manager Gareth Southgate embraced the tune as a way of raising money for his chosen charity, Macmillan Cancer Support.

[53] Viduka was a huge AC Milan fan as a kid as he grew up watching Marco van Basten, Frank Rijkaard and Ruud Gullit.