He competed at the 2009 World Championships and the 2010 World Indoor Championships without reaching the final. He ran at the 2011 Pan Arab Games but his sample came back positive for banned substances and he was banned for six months. He returned to competition at the 2012 Summer Olympic Games.
Al-Harthi won a bronze medal at the Asian Games in Guangzhou, China in the 100m, which was Oman's only medal in the Games. His personal best times are 6.67 seconds in the 60 metres, achieved at the 2010 World Indoor Championships in Doha. 10.17 seconds in the 100 metres, achieved in July 2011 in Manama. And 20.77 seconds in the 200 metres, achieved 2011 in Manama.