Stock write-downs and other charges pushed the Canadian firm to a net loss of $4.4 billion (£2.7bn) for the three months to 30 November. That compared with a modest net profit of $9m a year earlier.
Excluding one-off items, the firm, which abandoned an attempt to sell itself last month, reported a loss of $354m. Quarterly revenues fell to $1.19bn from $2.73bn as increased uncertainty about the company’s fate led to further sales erosion.
BlackBerry was at the forefront of mobile e-mail and for years its handsets were must-have devices for political and business leaders. But, in recent years, it has lost market share to Apple’s iPhone and competing Android-powered smartphones.
The firm said it had agreed a five-year deal with Foxconn Technology, the Taiwan-based maker of electronic products, to develop handsets.