Tasmanian Liberal senator David Bushby will be nominated as Australia's next consul-general in Chicago.
Senator Bushby on Friday announced his intention to resign from parliament on Monday, which would leave a seat vacant in the upper house.
"It has been an honour and a privilege to serve the people of Tasmania in the Australian Senate for over 11 years," Senator Bushby said in a brief statement.
"I look forward to commencing a new chapter in my professional career, following a short break with my family."
Just one hour later, Foreign Minister Marise Payne announced plans for the senator to take over from Consul-General Michael Wood in Chicago.
"Australia's economic links with the Midwest are integral to Australia's broader trade and investment partnership with the United States - our largest with any one country," the minister said in a statement.
"The Consulate-General in Chicago also engages leaders in government, education, culture and the media and provides consular and passport services to Australians who live in and visit Chicago and the Midwest."
Bilateral trade has grown from $42 billion to $70.2 billion in 2017-18, and two-way investment has more than doubled to $1.6 trillion in 2017 since the free trade agreement between the two countries.
Senator Bushby was chief government whip for the government in the Senate for the past four-and-a-half years, and was not up for re-election at this year's election.
Finance Minister Mathias Cormann thanked the senator for his "fine contribution" over the past 11 years.
He praised Senator Bushby as a "highly professional and competent" colleague, explaining these were reassuring traits when the government did not have a majority in the upper house.
"On behalf of all of my colleagues I would like to thank Senator Bushby for his contribution to Australia and his strong representation of Tasmania in the Senate," Senator Cormann said.
"I wish David and his family well for their future endeavours."
The Tasmanian parliament will decide on a new senator to represent the state.
