Qatar Airways is taking an almost 10% stake in Cathay Pacific to broaden its global reach.
The $661 million deal is expected to take place today in Hong Kong, making the Gulf carrier the third-largest shareholder in Cathay.
Qatar Airways already has a 20% stake in British Airways owner International Airlines Group, 10% of LATAM Airlines Group and 49% of Italian airline Meridiana.
However, a bid for part of American Airlines was rejected earlier this year. Swire Pacific owns 45% of Cathay Pacific and Air China 30%.
The Hong Kong-based airline is involved in a restructuring plan aimed at slashing HK$4 billion in costs over three years.
Cathay Pacific posted its worst first-half loss in 20 years in August.
Cathay Pacific and Qatar Airways both offered Hong Kong-Doha flights until February 2016, when Cathay dropped the route. Qatar Airways now flies to Hong Kong twice a day.
Qatar Airways group chief executive Akbar Al Baker said: “Qatar Airways is very pleased to complete its financial investment in Cathay Pacific.
“Cathay Pacific is a fellow Oneworld member and is one of the strongest airlines in the world, respected throughout the industry and with massive potential for the future.”