Zachary Rolfe shot Kumanjayi Walker, 19, three times in the remote community of Yuendumu, northwest of Alice Springs, on November 9, 2019.
Mr Rolfe was found not guilty of murdering Mr Walker following a high-profile, five-week trial in 2022.
He later became the subject of a wideranging coronial inquest into Mr Walker's death, which was told Mr Rolfe had previously been issued with a notice of the intention to stand him down from duty.
Mr Rolfe's lawyer Luke Officer confirmed on Wednesday that his client would appeal the decision to dismiss him.
"Constable Rolfe's intention is to ... exercise the full legal options available to him challenging the validity of the decision, the failure to afford fairness and the process by which it was made, the lawfulness of the decision, and also the merits of the decision," he said in a statement.
On Tuesday, the NT Police confirmed it had sacked Mr Rolfe over a breach of discipline.
"A 31-year-old male police officer has been dismissed from the Northern Territory Police Force effective April 4, 2023," a spokeswoman said.
"The officer was dismissed under section 78 of the Police Administration Act 1978 due to serious breaches of discipline during their policing career."
In March, NT police assistant commissioner Bruce Porter told the coronial inquest of the force's intent to retire Mr Rolfe based on psychological and risk assessments.
"We were of the opinion that he had the inability to continue as a member of the police force," he told the inquest.
The NT police force has been under [pressure over Mr Rolfe's dismissal.
Chief Minister Natasha Fyles is expected to hold a press conference after speculation Police Commissioner Jamie Chalker may be dismissed.
The NT police union, which had previously funded Mr Rolfe's legal fees, criticised the force's decision.
"The impact that the 9th of November 2019 has had on him, and many involved, has been difficult to fathom," NT Police Association president Paul McCue said.
"To be dismissed by the NT Police Force in these circumstances, once again, highlights deficiencies in police disciplinary processes."
Mr Rolfe had been on personal leave since August 2022.
He left Australia in February after writing a 2500-word open letter defending his character and criticising NT Police and its commissioner for how they handled the inquest.
"The coronial focus is still on me rather than on areas that could improve the circumstances of the NT," he wrote in the dispatch published in full on the "I support Zach Rolfe" Facebook page.
Mr Porter had told the inquest that police had served Mr Rolfe with a notice relating to the letter.
The inquest resumes later this year when Mr Rolfe is scheduled to give evidence, pending the outcome of his appeal against an earlier Supreme Court decision that he could be compelled to take the stand.