He won a gold medal in the 4 x 400 metres relay at both the 1996 and 2000 Summer Olympics and a silver medal in the 400 metres at the 2000 Summer Olympics. He is the twin brother of fellow Olympic medalist Calvin Harrison. At the 2000 Summer Olympics, Alvin Harrison and Calvin Harrison made history by becoming the first twins ever to compete and win Olympic gold medals together on the same relay team since the inception of the modern Olympic Games. In the 4 x 400 m relay, Alvin ran the first leg and Calvin ran the third leg. In 2008, the 2000 Sydney Olympics 4 x 400 metres relay US team was stripped of their medals after teammate Antonio Pettigrew admitted that he had used performance-enhancing drugs.
After his suspension expired in late 2008, Harrison enjoyed a late career renaissance via a transfer of allegiance to the Dominican Republic in 2008. He made the move following discussion with his wife and his track colleague Félix Sánchez, both of whom are Dominican. He competed for his new country at the 2009 World Championships in Athletics, running in the heats of the 400 m race. He made his second world appearance soon after and helped the Dominican 4×400-meter relay team to fourth place at the 2010 IAAF World Indoor Championships. Not only did Harrison run and compete for the Dominican Republic upon his return, Harrison also led the Federación Dominicana de Asociaciones de Atletismo (FDAA; Athletics Federation of the Dominican Republic) in the restructuring, reformation and implementation of the Dominican Republics first High Performance Olympic Development Program approved and welcomed by the Athletic Federation President Jose Rubio Ludwig. This new High Performance Olympic Development Program would benefit Luguelin Santos yielding the Dominican Republic the country's first ever Gold Medalist at the World Junior Championships in Barcelona, Spain. Luguelin Santos would go on to win the race in 44.85 seconds. In the same year, 2012, with continuous momentum Luguelin Santos dominated international competitors and surprised the world by becoming the country's youngest and world's youngest (18 year old) 400 metres silver medalist running 44.46 in the 2012 London Olympic Games. Leaving his impression on the Dominican Republic, Harrison was awarded with an Honorary Masters Degree in Exercise Science for his contributions and the successes thereof. Harrison has since retired from track and field and travels the country implementing High Performance Athletic Development Programs for various sports organizations and sports professionals including players in the N.F.L. and N.B.A. Alvin Harrison has four children: the son Shraee Harrison and three daughters; Shiyah Marie Harrison, Dejahna Harrison, and Anaia Harrison.