Former Commons aide to Miliband, Anne McGuire, said that after five years as the minister - and then the shadow minister - for the disabled, it was time to step aside and let someone else take on the role.
The MP for Stirling served as the opposition leader's parliamentary private secretary (PPS) for the first year of his party leadership and said that the experience had been "a pleasure and privilege".
She said she would continue campaigning as a backbencher against an "unprecedented attack" on disabled people by the Government and parts of the media.
McGuire said she asked in July to step down from the front bench at the next reshuffle, which is expected next week.
Miliband said: "Anne was a brilliant minister for the disabled, a fantastic PPS to me and a great member of the shadow front bench."