As of 2012[update], MacGregor is 1.58 metres (5 ft 2 in) tall and weighs 63 kilograms (139 lb). She attended Bournemouth School for Girls and is a member of Poole Yacht Club. She started sailing at the age of six in Poole Harbour.
MacGregor was candidate for selection for the 2008 Summer Olympics in the Yngling three-person keelboat class with crewmates Annie Lush and double Olympic gold medallist Shirley Robertson. Despite winning the bronze medal at the 2007 World Championships, the trio were overlooked for selection in favour of Sarah Ayton, Sarah Webb and Pippa Wilson who ended up winning gold in the Olympic event.
In 2010 MacGregor teamed up with her younger sister Kate MacGregor, Annie Lush and Mary Rook to win gold at the ISAF women's match racing World Championship in Newport, Rhode Island, United States. The British crew won the final 3–2 over an American team helmed by two-time world title-winner Sally Barkow. At the 2011 Sailing World Championships in Perth, Australia, MacGregor reached the final of the match-racing event, as part of a crew with Lush and Kate MacGregor, where they were beaten 4–0 by the United States boat skippered by Anna Tunnicliffe. The three won a gold medal at the 2011 World Cup event in Hyères, France by beating Barkow's crew 3–0 in the final.
MacGregor was selected to compete for Great Britain at the 2012 Summer Olympics in the newly created Elliott 6 metres match-racing event. She will compete alongside her sister Kate MacGregor and Annie Lush. Together the three are nicknamed the "Match Race Girls". The event will take place at the Weymouth and Portland National Sailing Academy with the round robin group stage being held from 29 July to 4 August 2012.
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- Leven, Kate (29 April 2011). "Lucy MacGregor's crew wins gold for Britain at Semaine Olympique Francaise in Hyeres". The Telegraph. Retrieved 12 July 2012.
- "London 2012: Luke Patience and Stuart Bithell picked in 470 class for Team GB". BBC Sport. 9 January 2012. Retrieved 12 July 2012.
- Al-Samarrai, Riath (9 July 2012). "Why three into one does go, for girls with a golden goal: Sportsmail takes a ride with the Match Racing Girls". The Daily Mail. Retrieved 12 July 2012.
- Warner, Michelle (10 July 2012). "Best of British Celebration Day with Skandia Team GBR At Cowes Week". Island Pulse. Retrieved 12 July 2012.
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- "Women's Elliott 6m". Official site of the London 2012 Olympic and Paralympic Games. Retrieved 12 July 2012.