Fish has won six tournaments on the main ATP Tour and has reached the final of four Masters Series events: Cincinnati in 2003 and 2010, Indian Wells in 2008, and Montreal in 2011. His best results at Grand Slam tournaments are reaching the quarter-finals of the 2007 Australian Open, the 2008 US Open, and the 2011 Wimbledon Championships. At the 2004 Olympics, Fish reached the final in the men's singles, losing to Nicolás Massú.
In April 2011, Fish overtook compatriot Andy Roddick to become the American No. 1 in the ATP rankings, reaching a career-high singles ranking of World No. 7 in August 2011.
Fish is the son of a tennis teaching professional and a housewife, Tom and Sally Fish. He was born in Edina, Minnesota. In 1984 a Minneapolis TV station ran a profile of Fish, at the age of two, hitting tennis balls from the baseline over the net. In 1986, Fish's family moved to Vero Beach, Florida. He attended Vero Beach High School for tenth grade, then moved to Boca Prep in Boca Raton, Florida, for his junior and senior years of high school. He, Andy Roddick, and Jesse Levine all attended Boca Prep International School.During 1999 he lived with Roddick's family, and the two played on the same tennis and basketball teams.