Weightman started out as a track runner but had her first success in cross country running, winning the under-23 section of the national championships in 2003. She took part in the Chiba Ekidenroad relay competition the following year and finished ninth. In 2006, she became a double national champion when she topped the podium in the 10,000 metres and half marathon events, and she returned to the Chiba Ekiden to improve to fourth place in her stage. Her first international championships appearance was at the 2006 IAAF World Road Running Championships where she placed thirty-seventh overall. Weightman ended the year by finishing second in the 10,000 metres at the Zatopek Classic behind New Zealander Jessica Ruthe. She represented Australia twice in 2007: taking forty-second place at the 2007 IAAF World Cross Country Championships and thirty-third at the 2007 IAAF World Road Running Championships. Weightman won a world championship medal at the 2008 IAAF World Cross Country Championships and she and Benita Johnson helped lead the Australian women to the team bronze. She made her marathon debut soon afterwards, finishing thirteenth in the women's race with a time of 2:32:32. This performance gained her selection for the women's marathon race at the 2008 Summer Olympics, where she finished thirty-third with a time of 2:34:16, the second best Australian performance after Johnson. Weightman improved her best world cross country performance at the 2009 IAAF World Cross Country Championships, finishing seventeenth and heading the Australian team to seventh place in the rankings. At the 2009 Christchurch Half Marathon, she was the first past the post to record her first major win on the road running circuit. She competed at her first World Championships in Athletics later that season as Australia's only participant in the women's marathon; she placed eighteenth overall and set a new personal best over the distance with a time of 2:30:42. She improved further in the marathon at the start of the following year, dominating the Nagano Olympic Commemorative Marathon from the 15 km mark to the finish. She knocked almost two minutes off her previous best time to win in 2:28:48, making her the first Australian to win the race. She was selected for the event at the 2010 Commonwealth Games in New Delhi. She fell away from the leading pack on two occasions but managed to make up the deficit both times and won the bronze medal in a time of 2:35.25, although she had to be taking from the finish line in a wheelchair due to her exhaustion. She won the 10 km run of the Gold Coast Marathon-event on 1 July 2012 in Gold Coast, Queensland, Australia finishing in front of Emma Moffatt. At the 2012 Summer Olympics, she finished in 17th place.
Personal life
Outside of competitive running, Weightman is a business consultant for IBM and she was the recipient of the 2000 Award for Business Excellence from The Age. She is the daughter of former footballer Peter Weightman and married her training partner, Lachlan McArthur, in 2008.
