Osoro represented Kenya twice on the world stage in 1991, running at the 1991 IAAF World Cross Country Championships (where he came fifth in the long race) and then on the track at the 1991 World Championships in Athletics (being eliminated in the 5000 metres heats by a narrow margin against Dionísio Castro). However, he won a medal in the 5000 m at that year's 1991 All-Africa Games. He featured in the Kenyan World Cross Country team for a second time at the 1992 IAAF World Cross Country Championships, although he was less successful on this attempt as he finished in 23rd place. Among his outings on the circuit, he won at the Belfast International Cross Country meet.