Castle reached one Grand Slam final in his career in the 1987 Australian Open mixed doubles event with Anne Hobbs. He won three ATP titles in men's doubles, as well as one title on the Challenger tour. He won $344,338 in prize money.
Between 2000 and 2010, Castle was a presenter on the now defunct ITV breakfast programme GMTV, sharing duties with Ben Shephard to present its weekday magazine programme. In 2009, he began presenting the ITV daytime game show Divided.
Castle was born in Epsom, Surrey. His mother, Lavinia Pollock (the great-grandchild of Annie Besant), was adopted shortly after her birth. She married Frank Castle in April 1953. The couple had five children: James; Richard, David, Fiona and Andrew, who was born in 1963.
Castle's father ran the fishmonger's in Westerham, Kent, where his customers included the lady of nearby Chartwell House, Winston Churchill's wife Clementine. He went on to own shops in North Cheam; Norbury; Stoneleigh, Surrey; and owned a fish and chip shop in Taunton, Somerset (Kingston Road).
At the age of nine, Andrew was asked by a friend to come and play tennis: "I can remember every detail about the day, from the feel of the ball to how it sounded when coming off the net. I insisted we played for eight hours non-stop." His parents supported him, but ran out of money, and his father was declared bankrupt, so both of them became taxi drivers. After winning the UK under-12 national tennis championships, Castle was given a full tennis scholarship to Millfield School in Street, Somerset.
Castle became a professional tennis player in 1986, after completing a marketing degree whilst on an athletic scholarship in the United States. During his playing career, he was regularly ranked number one in Great Britain. In 1986 Castle reached the third round at Queens Club. He won three tour doubles titles, and was a mixed doubles finalist at the 1987 Australian Open. His 1987 run at the US Open was his best career singles performance at a Grand Slam event, when he reached the third round by defeating David Pate and Jimmy Brown, before losing to Boris Becker in four sets. He represented Britain at the Seoul Olympic Games of 1988, and the Barcelona Olympic Games of 1992. Castle was a regular member of the British Davis Cup team and the European Cup team. His career-high rankings were World No. 80 in singles and No. 45 in doubles.
Castle represents Surrey at squash at over-45s level, and continues to play representative tennis around the world.
After retiring from professional tennis in 1992, Castle served as a commentator and presenter for BSkyB. As well as tennis, he presented basketball, motor racing and golf for Sky.
He joined GMTV in September 2000 as a presenter. After a decade, it was announced in June 2010 he was to leave the programme. Castle presented the final broadcast of GMTV on 3 September 2010.
He is a member of the BAFTA-nominated BBC tennis team, covering Wimbledon, the Aegon Championships at Queen's Club, the French Open, Australian Open and the Davis Cup. Castle has been lead commentator on all men's singles finals since 2003, working alongside John McEnroe, Boris Becker, Jimmy Connors, Tim Henman and John Lloyd.
In 2005, he presented the quiz show Perseverance; he presented two series of the teatime game show Divided (2009–2010); and appeared on Beat the Star on 24 May 2009 – all on ITV. He took part in ITV programme 71 Degrees North in 2010.
Castle previously presented the breakfast show on Smooth Radio and continues on the station with The Great American Songbook on Sunday evenings. He also presents a weekend morning show on speech-based radio station LBC.
Castle competed in the sixth series of the celebrity dance competition, Strictly Come Dancing. His partner was Ola Jordan. Castle's appearance marked the third time a main GMTV presenter had participated in the show. After week 4, he was placed 11th out of the remaining 12 contestants, with an average score of 22.5/40. Castle was voted out after round 7 of the competition on 2 November 2008. He scored 21 points for his samba, which placed him second from bottom on the judges' leader board. He appeared in the dance-off with Heather Small, who was saved by all four of the judges.
On 18 May 1991, Castle married former Japan Airlines air hostess Sophia, whom he had met in Tokyo whilst competing in the Japan Open tennis tournament. The couple have two children: Georgina (22) and Claudia (20). Georgina sang for the Great Ormond Street Hospital charity at the InterContinental Hotel in May 2008, and gained considerable attention from press and record companies. Both children were sports scholars at their schools. On 11 August 2009, Castle challenged Health Secretary Andy Burnham during an interview on GMTV, after news reports had cast doubts on the effectiveness of Tamiflu against the swine flu virus. He said: "I can tell you that my child — who was not diagnosed at all — she had asthma, she took Tamiflu and almost died." He is the great-great grandchild of Annie Besant, a prominent British socialist, Theosophist, women's rights activist, writer, orator and supporter of Irish and Indian self-rule, and the uncle of Sienna Nasir-Hawkins Chris Hawkins and Clare Nasir-Hawkins's daughter.
Other charities of which he is a patron or supporter include Brainwave, the Dan Maskell Tennis Trust, Great Ormond Street Children's Hospital, Macmillan Cancer Care, the NSPCC and Clic Seargent Cancer Care for Children.
In 2009, Castle became a Patron of the Festival4Stars talent competition. His daughter Georgina Castle was twice runner up in the national finals. She now attends the Central School of Speech and Drama in London.
In June 2013 Castle was forced into an official apology to former GB Davis Cup captain David Lloyd after suggesting he could be prevented from leading the Lawn Tennis Association due to 'personal problems'. His comments were made on air during a rain delay chat with Sue Barker at the Aegon Championships at Queen's Club in Kensington, London. As a result, he agreed to pay undisclosed damages to Mr Lloyd.