WARNING: This story contains details some readers will find distressing.
Max Loketi, 28, was working on a farming property at Hamel, south of Perth, in March when he picked up the small black cat and repeatedly hit it with a two-metre pole.
The footage of the attack, which was played in the Perth Magistrates Court, showed Loketi first holding the animal by the tail and then hitting it again when it was on the floor, barely moving.
Another person can be heard laughing in the background.
Loketi, who appeared in court on Wednesday via video link from Hakea prison and with the assistance of a Tongan interpreter, pleaded guilty to one charge of animal cruelty.
'Sustained and vicious'
RSPCA prosecutor Ian Weldon described the attack as "sustained and vicious" and said the footage of it was "distressing".
Mr Weldon said Loketi was charged after his employer, who had become aware of the social media video, reported the matter to police.
Loketi's lawyer, Gregory Chin, said his client had arrived in Australia eight months ago on a working visa and at the time of the incident was supposed to be in isolation because a colleague had tested positive to COVID-19.
Mr Chin said Loketi was not in his right frame of mind at the time and became infuriated when the animal, which was feral, attacked him near a toilet block.
The court heard he was from a small village in Tonga where Mr Chin said his upbringing included the hunting of wild animals.
Mr Chin said Loketi carried out the attack "in the most humane way he could".
Mr Weldon said while Loketi may have been taught to kill animals humanely during his upbringing in Tonga, "there was nothing humane about the way he dealt with the cat".
Mr Weldon said Loketi could be heard saying during the attack "do you know why I'm angry?" and "I'm going to smack the hell out of you."
The court heard the cat died, which Mr Weldon said was probably merciful.
Jail certain despite plea
Magistrate Joe Randazzo said he would take into account Loketi's early plea of guilty, his lack of any criminal record and the two weeks he had spent in custody away from his family in his consideration as to what penalty to impose.
But he said he also had to consider "the cruelty", "the torture" and "the malicious beating" Loketi had inflicted on the cat.
"I want to step back and have a think … [but] you will leave this video room today knowing I will be jailing you," Mr Randazzo said.
Loketi will be sentenced next week.
Tevita Fifita Vaenukut, who is accused of recording the attack, is yet to plead to the animal cruelty charge against him.
He is also due back in court next week.