Housing association Gentoo has been named as Stonewall's 2014 top gay-friendly employer, beating professional services giants Accenture and Ernst & Young, now known as EY, to the top spot.
The lesbian, gay and bisexual rights charity also revealed that Nottinghamshire Healthcare NHS Trust came second in Stonewall's workplace equality index and the Co-Operative came third.
Britain's military and security services are also well represented on the list, with the Security Service (MI5), Ministry of Defence, the Army and the Royal Navy all securing positions.
"Winning this award is an amazing achievement. It truly is the people at Gentoo that make this business great and it is vital that everyone feels able to be themselves at work and give us all they've got," said Peter Walls, chief executive of Sunderland-based Gentoo.
"This award will motivate us to continue to find new ways of working towards our vision."
Stonewall said Leicestershire County Council LGBT Workers' Group wins the award for Employee Network Group of the Year and Ministry of Defence is named Most Improved Employer of the Year.
The charity also revealed Andy Woodfield, head of International Development Consulting at PwC, is named Senior Champion of the Year. IBM wins the award for Global Employer of the Year.
Ben Summerskill, chief executive of Stonewall, said: "Gentoo and every single employer in the Top 100 has performed remarkably this year as competition for a place on the list of gay-friendly employers has never been fiercer."
He added: "This commitment from organisations - across 38 different industries – is changing the face of workplaces for the better for all staff - regardless of their sexual orientation."
The Top 100 list is based on the results of Stonewall's Workplace Equality 2014, the tenth published by the charity.
The Index is based on a range of key indicators which include a confidential questionnaire of lesbian, gay and bisexual staff, with over 9,700 participants.
Full results of the Stonewall Top Employers 2014 will be announced at a ceremony hosted on Wednesday evening at the Tate Britain.