The programme, run by the gay equality charity, helps employers to develop inclusive workplace cultures for their lesbian, gay and bisexual staff.
Balfour Beatty joins businesses as diverse as The Royal Navy, National Grid, Network Rail and major council clients, among over 650 employers in the scheme.
Other members include Arup, Kier Building Maintenance and Lend Lease.
Paul Raby, Chief HR Officer at Balfour Beatty said: “By supporting and developing our lesbian, gay and bisexual staff through the diversity champions programme we’re sending out a powerful message both to our existing and potential employees.
“We’re proud to join the programme and look forward to developing our work around sexual orientation.”
Chris Edwards, client group manager at Stonewall said: “Balfour Beatty is sending a powerful signal to lesbian, gay and bisexual people that it is an inclusive and progressive employer.
“By doing so, we are helping to drive positive change across the construction sector.”
Together with joining the Diversity Champions programme, Balfour Beatty is also setting up a network for lesbian and gay staff.
Matthew Flood, general counsel of Balfour Beatty’s support services division, is the group’s most senior openly gay employee.
In 2013 he was recognised by the Financial Times as number 40 on the Top 50 OUTstanding in Business List – a list of leaders from across the corporate world who stood up to be counted as inspirational role models for other staff.
Flood said: “It is up to senior leaders to make people feel it’s OK to be themselves.
“These are challenging times, and we need people around us who can see the world with different eyes, and tackle problems in different ways, particularly in the infrastructure world where the LGBT community has traditionally been under represented.”