Santiago Machuca was a member of the United States Army and served in both the Korean and Vietnam wars. During that time he earned distinctions as a pistol shooter and represented Puerto Rico in international competitions. He had his greatest success at the 1970 Central American and Caribbean Games, where he won gold in the 25 metres standard pistol event, while he just missed the podium in fourth in the 25 metres centre fire pistol competition at the 1971 Pan American Games. His only Olympic appearance came the following year, when he was 48th in the free pistol, 50 metres tournament in Munich.