Bellos was born in London to a Jewish mother, Renee Sackman, and a Nigerian father, Emmanuel Adebowale, who came from Uzebba and joined the merchant navy during the Second World War. Raised in Brixton, she was educated at Silverthorne Girls’ Secondary Modern School, Dick Shephard Comprehensive School and the University of Sussex. She married in 1970 and gave birth to two children, in 1974 and 1976, and came out as lesbian in 1980. Her marriage ended in divorce in 1983. She is now a grandmother. On 21 December 2005, she and her partner, Caroline Jones, were among the first couples to enter into a civil partnership in the UK, at Southwark Registry Office. She now lives in a small town near Norwich.
She was vice-chair of the successful Black Sections campaign to select African Caribbean and Asian parliamentary and local candidates within the Labour Party. In 1985 Bellos was elected as a Labour councillor to Lambeth London Borough Council and was leader of the council between 1986 and 1988. She was the second black woman to become leader of a British local authority, after Merle Amory in Brent. Bellos resigned as leader on 21 April 1988 after disputes within the Labour Party over the setting of the Council budget. She was a prominent figure in left-wing politics in London in the 1980s and was labelled by The Sun as a member of the 'Loony Left'. Bellos attempted to become a parliamentary candidate, without success, most notably for Vauxhall.
Bellos was the treasurer of the Africa Reparations Movement (UK). She was co-chair of the Southwark LGBT Network until February 2007 and an adviser to Southwark Council. From 2000 to 2003, she was co-chair of the LGBT Advisory Group to the Metropolitan Police. She remains a community activist and is a patron of Broken Rainbow, which supports LGBT people experiencing domestic violence.
As a lesbian feminist, Bellos argued strongly in the early 1980s that an inclusive approach to women’s issues must take account of social class, minority and majority ethnic identity, disability, sexual identity and religion. This approach was unpopular at the time but has since become accepted as equality law and social attitudes have changed. No longer regarded as ‘loony left’, Bellos now teaches employers and their staff to apply the Equality Act 2010, the Human Rights Act 1998 and other equality law. She has accomplished many firsts in her fight for equality, notably originating Black History Month in the UK whilst chair of the London Strategic Policy Unit. Bellos has worked on mainstreaming equality within many public bodies, including the British Army and the Metropolitan Police Service. She was an Independent Advisor to the Metropolitan Police, the Crown Prosecution Service, and the Association of Chief Police Officers.
She is a founder member and Chair of The Institute of Equality and Diversity Practitioners.
In 2023 Bellos appeared in the Channel 4 TV documentary 'Gender Wars', calling for a sensible debate about the clash between women's rights and trans rights.