Territory Alliance last night unveiled CLP stalwart Melanie Usher as its candidate for the poll.

Territory Alliance leader Terry Mills was in Katherine last night to announce Ms Usher would take on the CLP's Jo Hersey for the seat of Katherine.

Sitting candidate Sandra Nelson is not contesting the August poll after one term in office for the ALP.

Territory Labor has been searching for its own candidate and has even resorted to advertising outside its ranks but no candidate has been announced yet.

The CLP is looking to reverse the result after Willem Westra van Holthe's shock loss to the ALP's Sandra Nelson in the 2016 election by a handful of votes.

Ms Usher works in the office of Dr Sam McMahon for the CLP but it is understood she has taken a leave of absence while she contests the election.

The CLP selected Katherine businesswoman Jo Hersey as its candidate after a pre-selection battle with Ms Usher late last year.

The NT election will be held on August 22.

Meanwhile, allegations of a bloody physical altercation between Senator McMahon and her chief-of-staff Jason Riley are being investigated by the Country Liberal Party and Commonwealth Department of Finance.

The department and CLP have both been handed a formal complaint detailing allegations of misconduct within Senator McMahon's office.

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