The appointment of the 62-year-old, who has been credited with transforming education in Birmingham, as the Commissioner for London Schools ended months of speculation.
He will work alongside junior education minister Stephen Twigg on the Government's London Challenge, a push to raise results and co-ordinate policy across the city's 33 local education authorities.
Professor Brighouse will be based at London University's Institute of Education, where he is a visiting professor. He agreed to the pound;90,000-a-year commissioner's job on the condition he could spend only four days a week in the role.
He told The TES: "I pledge that if it turns out it cannot be done in that time I will be the first to say, 'Let someone do it full-time'.
"But I hope it can be."
His new post, which starts on January 1, may be greeted with some resistance from London LEAs who fear he could undermine their control over schools.
But Louisa Woodley, chair of the Association of London Government's education panel, said the city would benefit from the "dedicated leadership and additional resources" the new tsar and the London Challenge would bring.
And Professor Brighouse, Birmingham's former chief education officer, was keen to state that the boroughs were already doing excellent work, and his role was merely to support them.
"I have absolutely no power," he said. "This is not a new tier of management.
"My role is first and foremost about supporting the energy and expertise of staff already in London, and trying to help them, I think, like an honest broker."
He added that his key priorities would be raising secondary-school standards, making admissions arrangements across London fairer for parents, and finding ways to improve school buildings.
Kate Griffin, president of the Secondary Heads Association and head of Greenford high school in Ealing, had hoped Professor Brighouse would get the job.
"London heads would rather have him part-time than a lesser person full-time," she said.