Silent Witness star Emilia will kick off the five-part series playing the monarch as she was at 29 in an hour-long film.
Set in 1955, two years after the Queen's coronation, it will focus on the relationship between Princess Margaret and Captain Peter Townsend, and the British ruler's steps to convince her younger sister to call off their wedding plans.
Dramatised scenes in the series will be interspersed with news archive footage and testimony from royal insiders, including Penny Russell-Smith – the Queen's former press secretary who worked at the palace for 14 years until 2007 – who is acting as a consultant and interviewee.
The other actresses tackling the role are Samantha Bond, Susan Jameson, Barbara Flynn and Diane Quick.
James Bond star Samantha will take the lead in the second film, covering the attempted kidnap of the Princess royal in 1974 and the IRA threats at that time, and former Coronation Street actress Susan will play the Queen in the third, set in 1986 and based around the sanctions imposed on South Africa.
Cranford star Barbara is tasked with portraying Elizabeth during her 'annus horribilis' – 1992 – when Prince Charles and Princess Diana announced their separation and the Duke of York and the Princess Royal were divorced.
Finally Diane will star in the series' final outing, covering the marriage of the monatch's son and Camilla, the Duchess of Cornwall. The dramatisation does not cover the death of the Princess of Wales, which was the subject of Helen Mirren's Oscar-winning film, The Queen.
The series will be broadcast in November.