Former South Australian independent Senator Nick Xenophon has declared he will run for the Senate at the federal election, forcing his former party colleague Rex Patrick to rethink his re-election plans.

Confirming one of the worse kept secrets in politics, Mr Xenophon, who resigned from the Senate in 2017 for an unsuccessful run at state politics, said he “tried to be a political hermit” but “can no longer sit on the sidelines”.