The deal is set to be unveiled by British Prime Minister David Cameron on Wednesday at the start of a 24-hour visit to Indonesia aimed at boosting trade and investment.
Garuda is buying 11 units of the A330-300 that will be delivered in a timeframe between 2013 and 2017, said one source close to the deal, asking not to be identified.
The new jets would increase the number of long-haul A330s already delivered to Garuda or on order from the airline by two thirds and would be powered by UK-supplied Rolls-Royce
None of the companies involved agreed to comment.
The A330-300 sells for $231 million at catalogue prices, but airlines typically pay less than the official price.
(Reporting by Olivia Rondonuwu, Tim Hepher)