Pol Lt Paisarn Weerakijpanich, a duty officer at Suvarnabhumi Airport Police Station, said he was called to the airport at 11.20am where a foreigner was said to have jumped from the fourth storey walkway leading to gate 10 of the terminal, which is 16m from the ground.
The man, 64, was seriously injured and was rushed to a hospital but succumbed to his injuries.
Witnesses saw the man lounge around the area before he jumped over the walkway's metal railing and hit the ground below. An airport security guard tried to grab him while he was climbing the railing but failed to reach him in time, the officer said.
Pol Lt Paisarn said the deceased entered Thailand on Jan 16 and had booked a flight back to Canada on March 22 but it appeared he had decided to return early as witnesses said he had left his luggage on a trolley near gate 10 before jumping to his death.
Police are attempting to contact his family and inform the Canadian embassy, he added.
Since Suvarnabhumi airport opened in 2006, seven people have fallen to their deaths from the upper-floor walkways. Most were suicides involving foreigners who had domestic problems, including splitting up with their Thai wives.
Suicides have mostly occurred on walkways leading to gates 9 and 10 on the fourth floor. A few cases of people accidently falling after leaning over the metal railings have also occurred.
In October last year, the airport announced it would spend 33 million baht on 2.3m-high laminated glass barriers along the second and fourth storey walkways leading to 10 terminal entrances to stop people falling to their deaths or taking their lives from the passenger terminal.
They will be erected next to the original metal railings which are only 1.1m high. Pol Lt Paisarn said the spot where the Canadian jumped had not been equipped with the extra barriers yet.
An airport official, who spoke on condition of anonymity because she was not authorised to comment on the matter, said barriers had been partially installed at some of the walkways and the work was scheduled to be completed in May, but authorites would try to finish up in April following Sunday's suicide. The installation would be made at gates 9 and 10 deemed as risk spots first.
She declined to elaborate further on the progress of the barrier installation, saying officials would issue a press release on Monday.