Sir Brendan Barber, the former head of the TUC, has been appointed to the board of BT's infrastructure arm Openreach.
The former trade union chief and current chairman of Acas will join telecoms veteran Edward Astle as independent members of a newly formed board that will oversee "strategy, investment and service delivery" at Openreach.
BT has faced calls from rivals to separate Openreach, and in November Ofcom ordered a legal separation of the firm.
The communications regulator stopped short of forcing a full break-up and sale of Openreach and added it remained ''open'' to proposals from BT for a voluntary separation of the division.
The firm said on Wednesday that the reorganisation will create "increased operational and management independence for Openreach".
But an Ofcom spokesman said: "These changes fall short of our requirements for a legally separate Openreach that delivers for all of its customers. We intend to take our plans to the European Commission later this year."
Mike McTighe, chairman of Openreach, said: "I understand that customers sometimes feel let down by Openreach because we haven't always delivered the service they expect or that we hope to provide.
"We need to do more to rebuild trust and credibility. This will be the board's focus and we are currently in consultation with BT Group about agreeing the plan to deliver better service, broader coverage and faster speeds for consumers and businesses across the country."
Andy Kerr, deputy general secretary of the Communication Workers Union, said: "The CWU has been pushing for the company to appoint a worker representative to the new board of Openreach.
"We are therefore extremely pleased that they have decided to appoint Sir Brendan Barber."