Patterson will take up the role as chairman of Salesforce for Europe, the Middle East and Africa (EMEA) after he was sacked as chief executive of BT in June 2018 amid a loss of faith in his leadership by shareholders.
His ousting followed five years at the helm during which BT expanded aggressively into live TV sports broadcasting, acquired mobile operator EE and faced a fraud investigation into its Italian unit.
The telecoms giant itself is now in the middle of a turnaround involving job cuts and a move to a new headquarters in a bid to save money.
In late-August, media reports emerged that the firm was also considering the sale of its Irish corporate business to private equity firm Mayfair Equity Partners in a deal expected to be worth over €300mln.
In late-morning trading on Thursday, BT shares were 0.3% higher at 166.9p.