Born in Dublin, Garth is the daughter of Jonathan Garth and Anne-Marie McDonald, both of whom also played for Ireland. Her father was born in South Africa. Garth herself made her international debut in July 2010, in a one-off ODI against New Zealand. On debut, she was 14 years and 70 days old, making her the youngest Irishwoman to debut and the third-youngest overall. Several others have since debuted at younger ages. Garth went on to play six more ODIs in 2010, including at the 2010 ICC Women's Challenge in South Africa. That competition featured both 50-over and 20-over components, with Garth making her Twenty20 International debut in the latter, against Pakistan. Aged 14 years and 174 days, she became the youngest player of any country to appear in that format, beating the record set by the Netherlands' Miranda Veringmeier. Three of her Irish teammates – Elena Tice, Lucy O'Reilly, and Gaby Lewis – have since debuted at younger ages. Since making her debut, Garth has been a regular for Ireland at both ODI and T20I level. In ODIs, her most outstanding performance to date came in August 2012, when she took 4/11 from five overs against Bangladesh. Her highest score at that level was made during the same month, an innings of 39 runs against Pakistan. In Twenty20 Internationals, Garth has taken two three-wicket hauls – 3/6 against the Netherlands in August 2011, and 3/17 against Australia in August 2015. In November 2015, Garth was named International Women's Player of the Year at the Cricket Ireland Awards. In June 2018, she was named in Ireland's squad for the 2018 ICC Women's World Twenty20 Qualifier tournament. In October 2018, she was named in Ireland's squad for the 2018 ICC Women's World Twenty20 tournament in the West Indies. In Ireland's opening match of the tournament, against Australia, she made her 100th international appearance for the team. Following the conclusion of the tournament, she was named as the standout player in the team by the International Cricket Council. In August 2019, she was named in Ireland's squad for the 2019 ICC Women's World Twenty20 Qualifier tournament in Scotland. She was the leading run-scorer for Ireland in the tournament, with 100 runs in five matches. In June 2020, Garth accepted a two-year contract with the Victoria women's cricket team in Australia.
