The actress who played Martha in Baby Reindeer was a talented young actress named Maisie Williams. She was known for her role as Arya Stark in the hit series Game of Thrones. Williams brought her natural charm and energy to the role of Martha, capturing the spirit of the spirited young reindeer who was eager to prove herself. Williams also had a great sense of humor and brought a lot of fun to the set, making her a perfect fit for the role.