Fimmel's modelling career first began when he was spotted working out at a gym in the Melbourne suburb of Hawthorn by the flatmate of Matthew Anderson, a talent scout for the prestigious Chadwick Models agency. Fimmel headed overseas and was signed on the spot with agency LA Models in 2002 after walking into their office broke and barefoot. He then became the first male in the world to secure a six-figure deal to model exclusively for Calvin Klein for a year. He fronted CK's Crave men's fragrance campaign and modelled the brand's famous underwear. It was reported that one of his London billboards had to be pulled down after complaints from an auto club of traffic congestion and accidents by 'rubbernecking' female drivers, but Fimmel insisted the story started with a rumor spread on the internet. Fimmel appeared on magazine covers including France's Numero Homme and America's TV Guide, as well as on top-rating American TV shows in 2003 including Jimmy Kimmel Live!, The Sharon Osbourne Show, Live with Regis and Kathie Lee, MTV's Total Request Live and entertainment TV news program Extra. He also made a cameo appearance in the bar scene of a video clip for Janet Jackson's "Someone to Call My Lover" and played a hunk loading hay onto the back of a pick-up truck in Jennifer Lopez's "I'm Real" (not to be confused with her song of the same name featuring rapper Ja Rule). Fimmel has played a diverse spectrum of characters on the small and big screens. In 2008, he portrayed a murderer in Restraint and a party boy in Surfer, Dude with Matthew McConaughey and Woody Harrelson. In 2010, he portrayed a compassionate cowboy in Pure Country 2: The Gift and a forensic photographer in Australian horror movie Needle, co-starring Ben Mendelsohn. Fimmel was signed as the lead character in the television series Vikings, costarring Jessalyn Gilsig, Katheryn Winnick and Gabriel Byrne.
The actor’s favorite recreational activities include Australian rules football (AFL), camping, surfing, riding motorbikes and going to the beach.
Fimmel also played a celebrity cricket match in the 2009 Australia vs England Hollywood Ashes with fellow Australian actors Jesse Spencer (from House) and Cameron Daddo (from Models Inc.), plus celebrity chef Curtis Stone, INXS bass guitarist Garry Gary Beers and fast bowler Michael Kasprowicz.