Hayden won a bronze medal in the 100 m freestyle at the 2012 Summer Olympics in London with a time of 47.80, and was world champion in the same event in 2007 with Filippo Magnini of Italy.

[4] It was further worsened when Hayden was mistaken for a protester and beaten up and arrested by the riot police because he was "tall and wearing a dark shirt" the night before the Closing Ceremonies, a week after his competition ended.

[4][5] In Melbourne for the 2006 Commonwealth Games, Hayden won his first major international silver medal when he finished second in the 50 m freestyle, an event he had not intended on racing.

In the process of winning the gold, Hayden had also shaved down his own national record in the event down to 48.43 and he also added a bronze from the Worlds in the 4×200-metre freestyle relay.

Instead, his coach decided to rest him for the 4×100-metre freestyle, which was held that same day (Hayden set a Canadian record in the opening leg with a time of 47.56).

While Hayden was promoted as the best Canadian swimmer at these games with his world title, only fellow long-distance freestyle Ryan Cochrane managed to medal for the nation in the pool, while the remainder of the swim team failed to make the podium despite a general improvement over their 2004 showing.

The next season brought further success for Hayden as went on to touch out for the silver on a long glide in the 100 m freestyle final at the 2011 World Aquatics Championships.

After disappointment at the previous two Olympics when he failed to qualify for the 100 m final, he became the first Canadian to do so in swimming's glamour event since Dick Pound in 1960.

[2] Gold and silver went to American Nathan Adrian and world champion James Magnussen of Australia, while Hayden beat out Yannick Agnel and César Cielo for third; the medals were also presented by Dick Pound.

"[8] Hayden announced his retirement from the sport after the 4×100-metre medley relay at the Olympics but said he believed in the Canadian swim team to thrive in the future, saying that "I think in the grand scheme of things, with the people we have, we've done an amazing job … As long as we keep that momentum building, I think we're going to see more success come from more diverse events.

[11] After only 6 months of training, Hayden met the Olympic "A" Qualifying time with a 21.97 in the 50m freestyle at the TYR Pro Series in Des Moines, Iowa.

The onset of the COVID-19 pandemic resulted in the 2020 Summer Olympics being delayed by a year, which Hayden would later credit with giving him more time to return to competitive form.

[12] Hayden's return was widely credited for providing leadership to the men's program, with the most notable result being the surprise fourth-place finish in the 4x100 m freestyle relay where they were just 0.3 seconds behind the Australians who took the bronze medal, an event where the Canadian team had not been expected to even qualify for the final.