She was born in Parkes as Rachel (Trixie) McGirr, the daughter of Greg McGirr, a former short-term leader of the New South Wales Labor Party (March–July 1923). From an early age she was known as Trixie.
Trixie Gardner is a dentist by profession. She gained a Bachelor of Dental Surgery (BDS) in 1954 from the University of Sydney and later studied at Cordon Bleu de Paris. She was a councillor of Westminster City Council from 1968 to 1978, and was Lady Mayoress 1987-88.
In 1970, she stood for the Conservative Party against Barbara Castle (Labour) in Blackburn, and in 1974 stood against John Pardoe (Liberal) in North Cornwall. In 1971 she was made a Justice of the Peace.
On 19 June 1981 she was created a life peeress of the United Kingdom, taking the name Baroness Gardner of Parkes, of Southgate in Greater London and of Parkes in the State of New South Wales and Commonwealth of Australia. She was ennobled for her two decades of community and local government work in the Tory cause, the first Australian woman to be so honoured.
On 4 April 2007 she was made an Honorary Fellow of the University of Sydney.
Her husband was Kevin Gardner (1930-2007). He was also Australian-born. He was educated at Waverley College and won a scholarship to the University of Sydney to study dentistry, winning the Arnott Prize for oral surgery in 1954. He spent a year on the university teaching staff at the Sydney Dental Hospital before going to London in 1955. He married Trixie McGirr in 1956 in Paris, and they set up their home in London.
In May 1982, the year after she joined the House of Lords, Kevin was elected to Westminster City Council, where Trixie had been a councillor since 1968. He was the first Australian to be the Lord Mayor of Westminster. He was re-elected as a councillor in 2006 at the age of 75.
Their Catholic faith was central to their lives. They had three daughters. Kevin Gardner died in February 2007