Montagna is a hard running wingman who is known for his kicking ability and teamwork. He enjoyed a breakthrough season in 2006, only missing one match and gathering over 400 disposals for the season. He averaged 19 disposals a game, increasing his averages in both contested and uncontested possessions. He is a strong tackler.
In Round 8, 2007, in a match against Hawthorn, Montagna suffered a broken jaw but only missed one week with the injury. Although 2007 was the first since 2004 that the St Kilda side had missed out on playing in the finals series, it was the season that saw Montagna become a top line AFL footballer. Montagna played consistently throughout the season and continued the improvement he had shown in 2006. He played an accountable and hard running role through St Kilda's midfield, averaging 24 disposals and 3 tackles per game and kicking 10 goals for the year. Some of Montagna's highlights for the year included best on ground performances against the Kangaroos, Richmond and Hawthorn in the second half of the year. Montagna was rewarded for his efforts with a third place finish in St Kilda's 2007 best and fairest.
Montagna averaged 27.9 disposals and 6.25 tackles in 2009.
Montagna played in 21 of 22 matches in the 2009 aeason in which St Kilda qualified in first position for the finals series. He played in the 2009 AFL Grand Final in which St Kilda were defeated by 12 points.
Montagna played 26 games in 2010, including four finals, and averaged 28.6 possessions. He finished second in St Kilda's Best & Fairest Award (Trevor Barker Medal), and was selected in the AFL's All-Australian team for the second year in a row.
Montagna was involved in a police investigation of a woman's claims of being raped by St Kilda player, Stephen Milne at Montagna's house in 2004. No allegations were made against Montagna. Charges against Milne were not laid by the police at that time; however, the story resurfaced in June 2010 when a former senior detective, Scott Gladman, said that he was pressured to do the "right thing" by another police officer during the 2004 investigation and that the alleged victim's statements were released to the football club before the decision to drop the case was made. Milne was subsequently charged with four counts of rape and committed for trial on three counts of rape. In 2014 he married his girlfriend of four years, Erinn Byrne.