Cathay is one of the world's biggest cargo airlines, and its decision is expected to have a sizeable impact.
Previously, the airline had said it would only transport shark fin that was sustainably sourced.
Shark fin is considered a delicacy in Chinese cuisine and is often served as a soup at upmarket banquets.
More than 70 million sharks are killed every year, according to WWF figures. Large numbers are exported to Hong Kong, where they are consumed or further exported to mainland China.
"On the issue of shark's fin, with immediate effect we are happy to agree to ban the carriage," Cathay Pacific said in a statement on Wednesday.
It said it had not approved any shark fin shipments over the last year, pointing out that it had turned down 15 shipment requests for shark-related products.
Early reports said the ban extended to all shark products on cargo and passenger flights, but the airline told the BBC it currently applied to shark fin only,
Cathay said it would continue to review its policy.
Marine conservationists hailed Cathay's decision, with one proclaiming that it would make Hong Kong "proud".
"More Hong Kong businesses need to follow the lead," Hong Kong-based conservationist Sharon Kwok told AFP.
Government data cited by the South China Morning Post shows that shark fin imports to Hong Kong dropped by 42% between 2010 and 2015 to 5,717 tonnes.
During this period there was also a significant decline in imports by air.
Cathay now joins airlines including British Airways, American Airlines, Qantas, Singapore Airlines and Emirates in banning shark fin.

They are signed by "composer Mark Jones" and are posted from Lancashire.
Raffaele Hairdressing manageress Clare Harper said she was "bewildered" by the first one but had now received four, which she has framed.
She said they had become a talking point with customers, though her husband had asked if any of them "looked like they had a crush on her".
"I'm waiting for the next one coming, I'm practically on the doorstep now," she said.
The mystery author has been posting poems, written on black card in silver pen, around the country for more than five years.
He has sent five to a salon in Penygroes in Gwynedd and seven over three years to a salon in Lancashire.
There are reports of poems being sent to Yeovil Town and Hednesford Town football clubs, churches and salons in the north-east of England and hotels in Aberystwyth and Machynlleth in Mid Wales, among others.
They appear to be love poems and each include the phrase "keep your chin up, keep smiling".
Some recipients have attempted to find the poet but with no success.
Hong Kong-based airline Cathay Pacific has announced a ban on shipments of shark fin in a move that has been welcomed by conservationists.
[NEXT_CONCEPT]
A Hartlepool hair salon has joined a growing collection of businesses around the country being sent mystery poems.