Captain Mark Phillips was born on September 22, 1948, in Tetbury, Gloucestershire, England. Phillips attended Sandhurst Royal Military Academy and after graduation he entered the military, joining The Royal Dragoon Guards. While rising in the ranks from Lieutenant to Captain, Phillips was named a Commander of the Royal Victorian Order, in recognition of his service to the monarch of the British Royal Family, and a Personal Aide-de-Camp to the Queen, which allowed him to represent the ruling monarch and her viceroys.

Phillips began his eventing career in the Beaufort Hunt Pony Club, riding alongside Mike Tucker and under the Olympic gold medalist, Colonel Frank Weldon. He went on to win a team gold medal for Great Britain at the Munich Olympics in 1972 and was on the gold medal-winning British teams for the World Championships in 1970 and European Championships in 1971. Phillips won the Badminton Horse Trials four times, in 1971, 1972, 1974, and 1981. He also won Burghley in 1973 and represented Great Britain on two winning Nations Cup show jumping teams. Phillips retired from competing in 1988 after earning a team silver medal at the Seoul Olympic Games.

Following his retirement from competition, Phillips focused on his cross-country course design career. He designed the Burghley CCI4* course from 1989-1996, 1998-2000, and 2005-present, and also designed the Luhmuhlen CCI4* course for 12 years. In the U.S. he designed the USEA American Eventing Championships for several years and is currently the designer for several events including those held at the Tryon International Equestrian Center and the 2018 World Equestrian Games.

In 1994 Phillips took on the role of Chef d’equipe for the U.S. team and held that position for nearly 20 years. Under his guidance the U.S. won individual silver at the 1994 World Equestrian Games; individual gold and team silver at the 1995 Pan American Games; individual bronze and team silver at the 1996 Olympic Games; team bronze at the 1998 World Championships; individual silver and bronze and team gold at the 1999 Pan American Games; individual gold and team bronze at the 2000 Olympic Games; team gold at the 2002 World Equestrian Games; individual gold, silver, and bronze and team gold at the 2003 Pan American Games; individual silver and team bronze at the 2004 Olympic Games; individual bronze at the 2006 World Equestrian Games; individual gold, silver, and bronze and team gold at the 2007 Pan American Games; individual silver at the 2008 Olympic Games; and individual silver and bronze and team gold at the 2011 Pan American Games.

Phillips met his first wife, Princess Anne, the Princess Royal, while competing on the eventing circuit and the two married in 1973. They had two children, Peter and Zara. Zara would go on to become a top eventing competitor herself, winning individual gold at the 2006 World Equestrian Games and team silver at the 2012 Olympic Games. Phillips remarried to top dressage rider, Sandy Pfleuger, in 1997 and the two had a daughter, Stephanie.