The High Court is expected to officially declare Tim Storer the replacement for Nick Xenophon Team senator Skye Kakoschke-Moore.
Ms Kakoschke-Moore stood down in November over her dual citizenship status and was ineligible to reclaim her seat.
Nick Xenophon's parliamentary clout has taken a serious hit with the court awarding the Senate spot to Mr Storer, who incidentally quit the minor party last year and will sit as an independent.
The court's full bench on Tuesday unanimously found Mr Storer should not be excluded from a special vote count which will determine the seat.
The Australian Electoral Commission conducted the special vote on Thursday.
The hearing will take place after 4pm AEDT on Friday.