Lowe was born in Hartlepool, England, United Kingdom. Educated in Hartlepool, she attended High Tunstall College of Science followed by English Martyrs School and Sixth Form College.
She accepted an athletic scholarship to attend the University of Florida in Gainesville, Florida, United States, where she swam for coach Gregg Troy's Florida Gators swimming and diving team in National Collegiate Athletic Association (NCAA) competition in 2009 and 2010. She won three Southeastern Conference individual championships in butterfly events, and received eight All-American honors in two college seasons. After the 2010 college season, she returned to Britain, where she is currently based at the Swansea Intensive Training Centre in Wales with coach Bud McAllister, mentor to the triple Olympic champion of 1988, Janet Evans.
Lowe competed for Great Britain at the 2008 Summer Olympics in Beijing in two individual events, as well a British relay team. She finished sixth in the 100-metre butterfly final with a time of 58.06, and reached the semi-finals of the 200-metre butterfly, coming ninth with a time of 2:07.87. She was also a member of the British 4x100-metre medley relay team that came fourth in a European record time of 3:57.50.
Lowe, who at 14 was selected for the Smart Track squad of super talents formed by the then Britain Performance Director Bill Sweetenham. She also competed in the 2008 FINA Short Course World Championships, coming third in the 100-metre butterfly and women's 4x100-metre medley relay, as well as fourth in the 200-metre butterfly. She was also part of the women's 4x100-metre medley relay team that won the 2008 European Championships in a then European record.
As her father is Welsh, Lowe competes for Wales at the Commonwealth Games and won a bronze medal in the 100-metre butterfly in the 2010 Commonwealth Games in Delhi.
At the 2012 Summer Olympics in London, she competed for Great Britain. She finished sixth in the 200-metre butterfly final with a time of 2:06.80. She was also a member of the eighth-place British team in the 4x100-metre medley relay.
Lowe holds the British records for 100-metre and 200-metre butterfly at both long and short course. She set her long course times at the British Championships (which acted as a qualifier for the Olympics), where she came first in the 200-metre butterfly and second in the 100-metre (she later equalled her 100-metre mark at Beijing). Her short course times for 100-metre and 200-metre butterfly were achieved at the World Short Course Championships and the Middlesbrough Open respectively.
In February 2017 Jemma announced her retirement from professional swimming and is now a director at SwimPath