Born in Feilding, Sergent won a bronze medal at the 2008 Summer Olympics in Beijing, as part of the New Zealand team in team pursuit, together with Sam Bewley, Hayden Roulston, Westley Gough and Marc Ryan.

[5] Sergent, with several other riders, joined the former Leopard Trek team to form RadioShack–Nissan, ahead of the 2012 season.

[1] Sergent switched to track cycling for the 2012 London Olympics, where he and his teammates (Sam Bewley, Marc Ryan, Westley Gough) made themselves double Olympic bronze medalists.

[6] Sergent was hit by a neutral service car during the 2015 Tour of Flanders, an accident which kept him out of the sport for three months and resulted in him having three operations.

He subsequently signed a two-year deal with AG2R La Mondiale from the start of the 2016 season.