Ms Davies was one of two nominees for the position and defeated Kalgoorlie MP Wendy Duncan after a ballot held in the Nationals party room.
She said she was ready to take on the rigours of joining the party leadership team with recently appointed party leader Terry Redman, who took over the top job from Brendon Grylls last week.
Mr Grylls stood down from the position on November 17 because of family reasons. He will stay on as the member for Pilbara.
‘The Nationals have a proud 100-year history in WA and continue to evolve as a contemporary political party,’ Ms Davies said.
‘Under the leadership of Brendon Grylls, the party has moved into a new era of political representation for regional WA, through forming an alliance with the Liberal Government and delivering Royalties for Regions.’
Ms Davies said her attention would now turn to working alongside Mr Redman to ensure regional WA continued to receive political consideration.
Raised on a family farm at Yorkrakine, near Wyalkatchem, Ms Davies (35) was elected as the Member for Central Wheatbelt at the March 2013 State election after first representing the Agricultural Region in the Legislative Council from 2008.
Ms Davies’ appointment received the endorsement of Mr Redman, who said she was in line to receive a ministerial portfolio in the Cabinet. ‘Mia has demonstrated a tremendous capacity since joining Parliament five years ago and has now been endorsed by the party to fill a leadership role and serve as a minister,’ he said.