In 2012 Amos improved his National Senior Record to 1:43.11 during a race in Mannheim. He became champion at the 2012 World Junior Championships in Athletics, finishing in a new championship record of 1:43.79. In the 2012 Summer Olympics, Amos won a silver medal in the men's 800 m race, the first Olympic medal for his country. His time of 1:41.73 established a new World Junior Record behind the new World Record set by David Rudisha and is tied with Sebastian Coe for the third fastest individual ever.