While playing in the National Junior College Athletic Association, Harper was awarded the Golden Spikes award in 2010. Harper was drafted number one overall in the 2010 MLB Draft by the Washington Nationals. He made his MLB debut on April 28th 2012.  

He was named a candidate for the All Star Final Vote in 2012, facing off against David Freese and Michael Bourne. Harper would eventually make it as a member of the National League All Star Team.