Born in Mildura, Victoria, Justin Sedgmen and his older brother Ryan began their speedway careers at Mildura's Olympic Park Speedway on the infield junior track. Justin and Ryan teamed to win the 2005 and 2006 Australian Under-16 Pairs Championships, and Justin followed that up by winning again in 2007 with Dakota North. Justin Sedgmen finished the 2007 Australian Under-16 Championship at the Gold Coast Speedway in Queensland in equal first place with 13 points with Dakota North, but ultimately finished 3rd in the Final behind North and future Under-21 World ChampionDarcy Ward.
Senior career
In 2009 both Justin and Ryan signed a contract with Speedway Ekstraliga team Unia Leszno, but they did not start in the league. Before a 2010 season, Sedgmen signed to Hungarian Speedway Miskolc. He also rode for Swindon Robins in 2010 and 2011. In 2011, Justin Sedgmen won the Jack Young Solo Cup at the Gillman Speedway in Adelaide. Also in 2011, Sedgmen was part of the Australian Under-21 Team that won the second semi-final of the Under-21 World Cup. Australia withdrew from the Final in Balakovo, Russia due to travel cost and visa problems, along with Sweden and Great Britain. In 2012, Sedgmen rode for Redcar Bears in the Premier League, doubling up with Lakeside Hammers in the Elite League, but was dropped by the Bears in July after inconsistent performances. In 2012, Sedgeman won his first senior title, winning the Victorian State Championship at Undera Park. After sitting out the 2013 UK season, Sedgmen joined Edinburgh Monarchs in the Premier League in 2014, winning the league title with the team, and going on to ride for them for two seasons. Sedgmen won the 2014–15 Gillman Speedway Division 1 Solo Championship on 6 December 2014. He set the tone for the meeting in the first heat of the night with a time of 55.0 seconds, easily the fastest time of the night and only one-tenth outside Leigh Adams' almost 6 year old track record. Sedgmen finished a to date career best third place in the four round 2015 Australian Championship behind runaway winner Jason Doyle and runner-up Sam Masters. Sedgemen and reigning Australian U/21 ChampionMax Fricke both finished the series on 48 points, but was awarded third place after having finished in front of Fricke in each of the B or A Finals they contested against each other over the series. Also, Sedgmen qualified for the A final in both Round 1 at Gillman and again in Round 2 at Mildura while Fricke only qualified for the A final in Round 3 at Undera Park. Sedgmen's best A final result was second at Gillman behind Doyle while he finished third behind Doyle and 2012 World ChampionChris Holder at Olympic Park. Later in 2015, Sedgmen and Max Fricke were named as the two reserve riders for the 2015 Speedway Grand Prix of Australia which was held at the Etihad Stadium in Melbourne, although neither got to race on the night. A fortnight later Sedgmen raced in the Darcy Ward Tribute Meeting at Gillman in Adelaide to raise money for the injured Australian rider. Sedgmen won his semi-final to make the A final, but was excluded for breaking the tapes at the start of the final. In November 2015, Sedgmen rejoined Swindon Robins for the 2016 Elite League season, and signed to ride for Grindsted in Denmark. In 2015 he finished third in the Australian Solo Championship. In 2016 he signed to ride for Lokomotiv Daugavpils in the Polish first division, but didn't ride for them, and in June was loaned to Ekstraliga team Falubaz Zielona Gora. In December 2016 he won the Jason Crump Invitational at Kurri Kurri.
World Championships
2009 – 10th placed in the Semi-Final Two
2010 – qualify to the Semi-Final
Under-21 World Cup
2009 – 3rd placed in the Qualifying Round One
2010 – 2nd placed in the Qualifying Round One
2011* – Won Semi-final Two
* Australia withdrew from the 2011 U/21 WC Final due to the cost of travel and visa problems
