He has had a career in both business and public service. He is the founder of Superquinn supermarket chain, of which he remained non-executive president after his family sold out their interest in August 2005. Superquinn was known for its dedication to customer service and having pioneered a number of innovations, including Ireland's first supermarket loyalty card in 1993, SuperClub. It also introduced self-scanning of goods by customers in a number of its outlets (Reward Card SuperScan). Superquinn became the first supermarket in the world to guarantee the absolute traceability of all its beef from pasture to plate, using TraceBack, a revolutionary system developed at Trinity College, Dublin by IdentiGEN.
He became the chairman of the Interim Board for Posts and served as chairman of its successor An Post (the Irish postal administration) until 1989 – he also served on several other public authorities and boards. From 1993 to 1998, he chaired the steering committee which oversaw the development of the Leaving Certificate Applied version. He currently chairs the IBEC-sponsored business committee on better regulation, Sensible Rules. In 2006 he was appointed an Adjunct Professor in Marketing at National University of Ireland, Galway.
He is a former President of EuroCommerce, the Brussel-based organisation which represents the retail, wholesale and international trade sectors in Europe. Its membership includes over 100 commerce federations in 27 European countries, European and national associations representing specific branches of commerce and many companies. Also he serves on the board of directors of CIES – the Food Business Forum based in Paris as well as the American-based Food Marketing Institute.
In 2009, he worked with independent shops and helped them to revamp, modernise and stave off stiff competition from multi-national retailers. It aired as RTÉ's six-part television series, Feargal Quinn's Retail Therapy. A second series aired in 2011 while a third series aired in 2012.
In 2011, he fronted RTÉ's Local Heroes campaign in Drogheda, County Louth which an assembled team of experts to kick-start the local economy. It aired as RTÉ 1's six-part television series, Local Heroes – A Town Fights Back.
Quinn was first elected as a senator in 1993 from the National University of Ireland constituency and was re-elected in 1997, 2002, 2007 and 2011. He is a member of the Joint Oireachtas Committee on European Affairs, the Joint Committee on Finance and Public Service and is an Oireachtas member of the National Economic and Social Forum.
In May 2010, he introduced a Private Members Bill – the Construction Contracts Bill 2010 – to protect building sub-contractors.
In May 2013, with Senator Katherine Zappone and Senator Mary Ann O'Brien, he introduced the Seanad Bill 2013 to reform the system of electing the elected members of Seanad Éireann (as provided for in Article 18.10 of the Constitution of Ireland) through a one person, one vote franchise.