Senator Small was sworn in during a ceremony in the upper house chamber on Monday.

The Bunbury-based bar owner also worked as a manager of production logistics at Woodside before he was picked to fill the casual vacancy.

Mr Cormann quit his role as government Senate leader last month to pursue the role of secretary-general of the OECD.

Senator Small will be third on the Liberals' WA Senate ticket for the next election behind frontbencher Michaelia Cash and government whip Dean Smith.

Australian Associated Press