"Fairfax Financial Holdings has agreed to purchase, through its subsidiaries, an additional USD 250 million principal amount of six per cent unsecured subordinated convertible debentures of BlackBerry," BlackBerry said in a statement.
The transaction will be completed on or before January 16, 2014, it added.
The Prem Watsa-led firm is exercising a previously announced option linked to BlackBerry's recent USD 1 billion debt financing.
Fairfax owns a 9.9 per cent equity stake in BlackBerry.
For the third quarter ended November 30, 2013, the company's revenues declined 56 per cent to USD 1.19 billion.
Following the decision, the struggling handset maker has undergone a series of changes. Its CEO Thorsten Heins was replaced by John Chen. It also replaced COO Kristian Tear, CMO Frank Boulben and CFO Brian Bidulka as part of the reorganisation.
It has recently appointed Ron Louks as President, Devices and Emerging Solutions, who will report to Chen.