Passengers on board the aircraft said they feared for their lives when Marks rushed towards the cockpit shouting that he wanted to "blow the plane up".
A passenger stood up, grabbed a flight attendant by the arm and told the 337 passengers aboard the Kuala Lumpur-bound plane that he had a bomb, witnesses said.
Flight 128 was about 10 minutes into a trip from Melbourne when Marks walked from his economy seat to the cockpit door holding an electronic device and threatened to blow up the jetliner, sparking panic among the passengers.
Mr Kok, who had been living in Melbourne for the past 30 years, said the situation at the airport was back to normal, and some passengers managed to get on another flight to Kuala Lumpur.
"There appears to be no imminent threat to passengers, staff or public and the investigation is ongoing", Victoria Police said in a separate statement.
Marks has a history of psychiatric illness and had just been released from a psychiatric facility, before he boarded the flight, police said.
"We are no longer treating it as a counter terrorism incident", he said. After waiting for almost an hour a half, heavily armed officers took over the plane. The staff was telling him to sit back down, upon which he threatened to "blow the plane up".
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Police praised the "heroic" actions of the passengers and crew.
The plane, which was headed to Kuala Lumpur, made an emergency landing back to Tullamarine Airport after fearless passengers tackled the man on Wednesday night.
Of the passengers who then overpowered the man, he said: "I can not tell you their names but they are good fellas".
"We pushed the guy onto the floor and cabin crew put cords on him and secured him to the ground.", he told the Sydney Herald.
"I thought the plane was going to go down, I thought the bomb was going to go off".
The incident came just months after Canberra called off the search for missing Malaysia Airlines Flight MH370 after a vast underwater hunt off Australia's west coast failed to find the plane.
Victoria Police Senior Constable Adam West said police responded to Malaysia Airlines request for help and arrived at Tullamarine Airport at 11:40 p.m. local time, according to News Corp Australia Network.
The Sri Lankan was eventually arrested after the plane, which was carrying 300 passengers, touched down at the Melbourne Airport. Malaysia Airlines Flight 17 was shot down over the Ukraine in 2014 with the loss of all 283 passengers and 15 crew.