Garner was raised on a dairy farm in Leitchville and completed his High School Certificate (HSC) at Cohuna High School in 1989.
Garner undertook tertiary studies at Melbourne University, graduating with a Bachelor of Commerce (Honours) and undertaking a postgraduate Honours year in Economics.
Garner has had significant experience in working in politics, as an Electorate Officer for Senator Julian McGauran and Ministerial Advisor to the Hon. Bill Baxter in the Roads and Ports portfolio. In addition, Garner was the Young Nationals State President for two years, the National Party Victoria Junior Vice President for a year, undertook a delegation to Shanghai, China as part of the Young Leaders Conference and completed a Political Exchange Tour of Japan. In 2021, Garner was elected to the Victorian Farmers Federation Water Committee.
Currently, Garner and his wife are busy running their businesses in Cohuna, Leitchville and Gunbower, as well as irrigated beef farms in Cohuna and Leitchville.