Singapore Airlines will acquire an additional 9.9% stake in Virgin Australia for A$123 million ($126 million), bringing its total stake to 19.9%.
"The strategic stake will be acquired through the purchase of shares held by the Virgin Group," SIA said in a statement.
The deal will see it buy 255.5 million shares at 48 Australian cents per share. Australia's Foreign Investment Review Board will need to approve the sale.
"Our partnership with Virgin Australia has been going from strength to strength, offering a wide range of consumer benefits," said SIA chief executive Goh Choon Phong.
This is SIA's second stake purchase in Virgin Australia in the last year. In November 2012, it purchased a 10% stake for A$105 million.
SIA does not have a seat on Virgin Australia's board. In regard to whether it will get a seat subsequent to the current deal, an SIA spokesman told Flightglobal that this is "up to the Virgin Australia board".
In 2011, SIA and Virgin Australia announced a partnership under which they cooperate in areas such as codesharing, reciprocal frequent-flyer programme benefits and lounge access, schedule coordination, and joint sales and marketing distribution.