Samuels was born in 1988 to mother Tracy Samuels and father Mark Samuels. She is the second eldest of 4 children and the family grew up in Merrylands, a suburb of Sydney and started athletics at Greystanes Little Athletics club.
Her first global appearance came in the shot put at the 2003 World Youth Championships at the age of fifteen, at which she finished 13th in the qualifying rounds. She returned to the competition two years later and demonstrated her potential by winning the bronze medal in the shot put with a new personal best throw of 15.53 m, but she showed that her abilities were also well-suited to the discus as she took the gold medal in that competition. Samuels also took part in the Australian Youth Olympic Festival in 2005, winning the shot put and taking second place in the discus throw.
The following year she opened her season with an appearance at the 2006 Commonwealth Games – her first major senior championship. She reached the shot put final, finishing twelfth overall, but again it was in the discus where she excelled, winning the bronze medal at the age of seventeen. She threw a discus personal best of 60.63 m to take home the title at the 2006 World Junior Championships and was seventh overall in the shot put. Following this, she opted to focus solely on the discus throw at major tournaments. She closed the year with a sixth place performance at the 2006 IAAF World Cup, representing Oceania.
She achieved a personal best throw is 65.44 metres at the World Championships in Berlin on 21 August 2009, winning her the gold medal. Samuels took part in the final edition of the IAAF World Athletics Final, but she was past her season's peak form and took fifth place with a sub-60 metre throw. She started strongly the following year, opening her season with a personal best of 65.84 m to win at the Sydney Track Classic in February. She gave a consistent series of throws at the 2010 Australian Championships and won her sixth consecutive national title (indoor and out) with a best throw of 63.31 m.