It's the first known investment by a Middle Eastern airline into an east Asian carrier.
Kingboard Chemical said in a statement to the Hong Kong exchange on Monday it sold its shares in Cathay Pacific for HK$5,162,266,000 (A$865.3 million), or HK$13.65 per share. The airline cut 600 jobs in May as part of measures to rebound from its losses.
Qatar Airways Group Chief Executive, His Excellency Mr Akbar Al Baker said, "Qatar Airways is very pleased to complete its financial investment in Cathay Pacific". "We already work together closely as fellow members of the Oneworld alliance, and we look forward to a continued constructive relationship", said Rupert Hogg, chief executive officer, Cathay Pacific.
Earlier in 2017, Qatar had planned to buy into American Airlines, but the idea was dropped after the USA carrier expressed little enthusiasm for the deal.More news: Socialism, capitalism and Trump Jr's Halloween candy
Qatar Airways' investment strategy has seen it acquire 20 per cent of British Airways-parent International Consolidated Airlines Group, 10 per cent of South America's Latam Airlines Group and 49 per cent of Italy's Meridiana.
Doha-based Qatar Airways has taken a 6.9% stake in Cathay Pacific.
Cathay's shares fell 1.7 per cent to HK$12.98 in afternoon trading after slumping as much as 4.9 per cent in the morning session.
Earlier this year it made a bid to buy 10 percent in American Airlines, the United States' largest carrier, but the deal went sour and Qatari officials eventually said that "it no longer met" Qatar Airways' goal. Cathay is 45 percent owned by Hong Kong conglomerate Swire Pacific.