BT is to cut 13,000 jobs over three years, about 12% of its workforce, as it seeks to slim down its management and back-office roles.
The telecoms giant said that the job cuts and other measures would help it to reduce costs by £1.5bn.
It added that it would be hiring about 6,000 employees to “support network deployment and customer service”.
A third of the job reductions will come from outside the UK in its Global Services division.
Last year, BT was forced to write down the value of the Italian part of Global Services after an accounting scandal that cost the firm more than £500m.
The company also said it intended to move out of its existing central London headquarters and into smaller premises.
BT forecast a fall in revenue of about 2% for the 2018-19 financial year. It also said it was keeping its full-year dividend unchanged from last year at 15.4p a share and would freeze it for the next two years.
Shares in BT fell nearly 8% in early trading.
Philippa Childs, national secretary of the Prospect union, said the announcement was “a devastating blow to managers and professionals represented by Prospect”.
She said Prospect had been working closely with BT on looking at the impact of organisational changes, but the number of job cuts sounded “unrealistic”.
BT said it was responding to changes in the telecoms market, including “increasing competitive intensity from established companies and new entrants”.
“It is critical that BT transforms its operating model to build a lean and agile organisation that delivers sustained improvement in customer experience and productivity,” it said.
The announcements came as BT disclosed that its annual pre-tax profits rose 11% to £2.6bn in the year to March.
The firm also announced a 13-year plan to plug its £11.3bn pension fund deficit, including regular payments into the scheme and a bond issue.