The Green Party leader, Caroline Lucas, has joined the Accord Coalition which seeks to reform faith schools and make them more inclusive.
The news comes at the Green Party kicks off its annual conference in Sheffield.
The MP joins bishops, teaching unions, humanists, and a range of groups who seek an end to discrimination in employment and admissions.
Caroline Lucas told the Accord Coalition: "The current legislative regime around faith schools allows religious discrimination on religious grounds in their pupil admissions and employment of teachers, and for them to provide their pupils with a narrow education about the range of beliefs held in society.
"These laws should be changed so that schools are open to children of every background, no matter what their parents’ or their own beliefs, open to all teachers qualified to teach in them, and to ensure that children learn about the beliefs of others, thereby better preparing them for life in an increasingly diverse society.
"This is therefore why I am delighted to support and join the Accord Coalition. Schools should not be a source of social division, but be as diverse a place as the local community from which they draw their pupils and aid the growth of mutual understanding".
Chair of the Accord Coalition, Rabbi Dr Jonathan Romain MBE said: "We are delighted to welcome Caroline as a Distinguished Supporter. Her support not only further strengthens Accord’s voice, but further highlights the breadth of concern that is felt about issues of religious and ethnic discrimination and segregation in our schools".
Caroline Lucas joins Accord’s growing list of supporters, who come from a wide variety of different political and religion and belief backgrounds. They currently include Baroness Tessa Blackstone, former Minister for Education and Vice-Chancellor of the University of Greenwich, the Rt Rev Richard Holloway, former Bishop of Edinburgh, Naomi Long, the first MP from the Alliance Party of Northern Ireland to be elected to the House of Commons, author Philip Pullman, Polly Toynbee and the Rev Professor Christopher Rowland, theologian at the University of Oxford.