[1] Millar grew up on a family property in the Central Highlands region, attending school in Capella and Emerald.
[2] After spending a decade working in the Emerald area, Millar was employed a rural reporter for ABC Local Radio for nine years.
[2] He then operated a small business on the Sunshine Coast where he worked as a public relations manager for Maroochy Shire Council for six years and unsuccessfully stood as a Division 7 councillor in the Sunshine Coast Regional Council local government elections in 2008.
[2][3][4] Prior to being elected, he worked as a media advisor to Mike Horan, Lawrence Springborg and John McVeigh.
[7] In November 2020, Millar was named as Assistant Shadow Minister to the Leader of the Opposition.