Harrington was born in London. Her father was Brigadier Bryan Fowler, an officer in the British Army, and her mother was Mary Walford. Bryan Fowler was originally from Kells, County Meath and served with the Royal Artillery in both World Wars, and married Mary, who was a widow, in 1944. She had two children from her previous marriage. Harrington had an older brother, John Fowler, who was also a racehorse trainer and died in an accident in 2008. Bryan Fowler left the army in 1949 and returned with his family to Ireland where Harrington spent her childhood. She did not go to school until she was aged twelve, being tutored. She then went to school at Hatherop in England for four years before going to a Finishing school in France.
Harrington and her husband Johnny Harrington both shared a love for horses. She was married to him until his death from cancer in April 2014. Johnny owned a racehorse and was a bloodstock agent. Together the couple had four children: James and Tara and Johnny’s from a previous relationship; Emma and Kate. As well, Jessica and Johnny had three sons-in-law, a daughter-in-law and seven grandchildren.
Even before Harrington got her training permit in 1989, she had earned a reputation for being one of Ireland's top three-day event riders. She represented her country with credit on three levels: European, World and Olympic. In 1994, Harrington’s horse Oh So Grumpy earned himself (and indirectly Harrington) a “landmark success” at the Galway Hurdle. A couple of years later Dance Beat picked up Leopardstown's Ladbroke Handicap Hurdle. By 1996 Harrington had earned a reputation for being linked to high profile horses. She then went on to enjoy seven Cheltenham Festival victories, rendering her "one of the most successful current Irish trainers at the meeting." Her most notable horses include: Moscow Flyer, Curtain Call, Bible Belt, Pathfork and Laughing Lashes. On 17 March 2017 she won the Cheltenham Gold Cup with Sizing John. Exactly one month later on 17 April Harrington won the Irish Grand National at Fairyhouse racecourse. It was a first win, in both races, for both Harrington and local rider Robbie Power.
Major National Hunt wins
|17 April 2017||Fairyhouse||Irish Grand National||Grade A||Our Duke|
|17 Mar 2017||Cheltenham||Timico Cheltenham Gold Cup||Grade 1||Sizing John|
|Apr 2013||Punchestown||Herald Champion Novice Hurdle||Grade 1||Jezki|
|Apr 2013||Fairyhouse||Weatherbys Ireland GSB Hurdle||Grade 3||One Fine Day|
|Dec 2012||Leopardstown||Paddy Power Future Champions Novice Hurdle||Grade 1||Jezki|
|Nov 2012||Fairyhouse||Royal Bond Novice Hurdle||Grade 1||Jezki|
|Nov 2012||Naas||Fishery Lane Hurdle||Grade 3||Jezki|
|Mar 2011||Cheltenham||RSA Chase||Grade 1||Boston's Angel|
|Feb 2011||Leopardstown||Deloitte Novice Hurdle||Grade 1||Oscars Well|
|Feb 2011||Leopardstown||Dr P J Moriaty Novice Chase||Grade 1||Boston's Angel|
|Feb 2011||Navan||Flying Bolt Novice Chase||Grade 2||Saludos|
|Dec 2010||Leopardstown||Fort Leny Novice Chase||Grade 1||Boston's Angel|
|Dec 2010||Navan||Navan Novice Hurdle||Grade 1||Oscars Well|
|Apr 2010||Punchestown||Motivate Challenge||Grade A||Chasing Cars|
|Feb 2010||Doncaster||Bluesquare.com Mare's Hurdle||Grade 2||Zarinava|
|Feb 2010||Navan||Johnstown Novice Hurdle||Grade 2||Coole River|
|Jan 2010||Leopardstown||Synergy Security Novice Hurdle||Grade 2||Coole River|
|Jan 2010||Leopardstown||MCR Novice Chase||Grade 2||Roberto Goldback|
|Jan 2009||Leopardstwon||Synergy Security Novice Hurdle||Grade 2||Roberto Goldback|
|Feb 2008||Leopardstown||betchronicle.com Spring Juvenile Hurdle||Grade 2||Personal Column|
|Mar 2007||Cheltenham||Weatherbys Champion Bumper||Grade 1||Cork All Star|
|Apr 2007||Fairyhouse||Dan Moore Memorial Handicap Chase||Grade A||Gemini Lucy|
|Nov 2007||Cheltenham||Champion Bumper||Grade 1||Cork All Star|
|Nov 2006||Fairyhouse||Royal Bond Novice Hurdle||Grade 1||Hide The Evidence|
|Apr 2006||Punchestown||ACC Bank Champion Hurdle||Grade 1||Macs Joy|
|Feb 2006||Gowran Park||Red Mills Trial Hurdle||Grade 2||Macs Joy|
|Jan 2006||Leopardstown||Pierse Hurdle||Grade B||Studmaster|
|Apr 2005||Aintree||Mumm Melling Chase||Grade 1||Moscow Flyer|
|Mar 2005||Cheltenham||Queen Mother Champion Chase||Grade 1||Moscow Flyer|
|Feb 2005||Leopardstown||AIG Champion Hurdle||Grade 1||Macs Joy|
|Feb 2005||Leopardstown||Dr P J Moriaty Novice Chase||Grade 1||Carigeen Victor|
|Feb 2005||Leopardtown||Irish Arkle Trophy||Grade 1||Ulaan Bataar|
|Dec 2004||Leopardstown||December Festival Hurdle||Grade 1||Macs Joy|
|Dec 2004||Sandown||Tingle Creek Chase||Grade 1||Moscow Flyer|
|Nov 2004||Navan||Fortria Chase||Grade 2||Moscow Flyer|
|Apr 2004||Punchestown||BETDAQ.com Champion Chase||Grade 1||Moscow Flyer|
|Apr 2004||Aintree||Mumm Melling Chase||Grade 1||Moscow Flyer|
|Apr 2004||Fairyhouse||Menolly Homes Handicap Hurdle||Grade A||Macs Joy|
|Dec 2003||Sandown||Tingle Creek Chase||Grade 1||Moscow Flyer|
|Nov 2003||Navan||Fortria Chase||Grade 2||Moscow Flyer|
|Mar 2003||Cheltenham||Queen Mother Champion Chase||Grade 1||Moscow Flyer|
|Mar 2003||Uttoxeter||Midlands Grand National||Listed||Intelligent|
|Mar 2003||Cheltenham||County Hurdle||Grade 3||Spirit Leader|
|Feb 2003||Newbury||Tote Gold Trophy||Grade 3||Spirit Leader|
|Dec 2002||Sandown||William Hill Handicap Hurdle||Listed||Spirit Leader|
|Apr 2002||Punchestown||Swordlestown Cup||Grade 1||Moscow Flyer|
|Mar 2002||Cheltenham||Arkle Trophy Chase||Grade 1||Moscow Flyer|
|Dec 2001||Leopardstown||Denny Gold Medal Novice Chase||Grade 1||Moscow Flyer|
|Apr 2001||Punchestown||ACC Bank Champion Hurdle||Grade 1||Moscow Flyer|
|Apr 2001||Gowran Park||Kinloch Brae Chase||Grade 2||Slaney Native|
|Nov 2000||Punchestown||Morgiana Hurdle||Grade 2||Moscow Flyer|
|Apr 2000||Punchestown||Champion Novice Hurdle||Grade 1||Moscow Flyer|
|Mar 1999||Cheltenham||Grand Annual Handicap Chase||Class B||Space Trucker|
|Mar 1998||Uttoxeter||Midlands Grand National||Listed||Miss Orchestra|
|Apr 1996||Punchestown||Champion Novice Hurdle||Grade 1||Dance Beat|
|Apr 1994||Galway||Galway Hurdle||Grade 2||Oh So Grumpy|
Major Flat wins
|Sep 2010||Curragh||Vincent O'Brien National Stakes||Group 1||Pathfork|
|Aug 2010||Curragh||Futurity Stakes||Group 2||Pathfork|
|Aug 2010||Curragh||Debutante Stakes||Group 2||Laughing Lashes|
|Jun 2009||Curragh||Ballygallon Stud Stakes||Listed||Long Lashes|
|Apr 2009||Navan||Navan Sprint Stakes||Listed||Jumbajukiba|
|Sep 2008||Curragh||Ascon Rohcon Solonaway Stakes||Group 3||Jumbajukiba|
|Jul 2008||Curragh||Keeneland Minstrel Stakes||Group 3||Jumbajukiba|
|Jun 2008||Down Royal||Specsavers Ulster Derby||Premier H'Cap||Fantoche|
|Apr 2008||Curragh||Castlemartin Galdness Stakes||Group 3||Jumbajukiba|
|Oct 2007||Curragh||Irish Cesarewitch||Premier H'Cap||Sandymount Earl|
|Sep 2007||Curragh||Juddmonte Beresford Stakes||Group 2||Curtain Call|
|Sep 2007||Curragh||Ladbrokes.com Solonaway Stakes||Group 3||Jumbajukiba|
|Aug 2007||Cork||Platinum Stakes||Listed||Jumbajukiba|
|Jul 2007||Curragh||Budweiser Premier Handicap||Premier H'Cap||Jumbajukiba|
|Jun 2005||Curragh||Balanchine Stakes||Listed||Sahara Princess|
|Oct 2004||Curragh||C.L Weld Park Stakes||Group 3||Jazz Princess|
|May 2002||Curragh||Tote Premier Handicap||Premier H'Cap||Evening Scent|
|May 2002||Curragh||Betdaq Premier Handicap||Premier H'Cap||Private Ben|
- Clower, Michael (2007). Kings of the Turf. London: Aurum. pp. 191–205. ISBN 1845132793.
- Mathieson, Amy. "Irish racehorse trainer John Fowler killed by falling tree". horseandhound.co.uk. Retrieved 2 February 2015.
- O'Hehir, Tony. "Henderson leads tributes to Johnny Harrington". Racing Post. Retrieved 13 January 2015.
- Anderson, Nicola. "World of horse racing comes out in force to pay respects to two stalwarts". Irish News. Retrieved 13 January 2015.
- "Jessica Harrington". British Champions Series. Retrieved 25 November 2017.
- "Meet Jessica Harrington". Jessica Harrington. Retrieved 25 November 2017.
- "Juvenile Filly Laughing Lashes Captures Group 2 stakes". Runnymede Farm. Retrieved 13 January 2015.
- "Duke Takes Irish National In Impressive Style". 17 April 2017. Retrieved 11 March 2018.
- "Jessica Harrington". British Champions Series. Archived from the original on 23 December 2015. Retrieved 13 January 2015.