Barker was born in
Islington to parents from Ireland and
Montserrat. She joined her sister Harriet in the foster care system just after she was born, and the two were adopted. Barker spent her early childhood in
London and
Winchester before growing up in
Glasgow until her teen years. While living in Glasgow, she took weekend classes at the Elizabeth Murray School of Dance. Her earliest acting experience was in an
RBS advertisement. Her parents eventually separated, and Barker moved to
Church Fenton, a village in the
Selby District of
Yorkshire, with her mother and stepmother. She attended
Tadcaster Grammar School nearby. She planned to study international relations at the
London School of Economics after taking a gap year, but decided to pursue
drama instead. She worked at the
National Railway Museum in
York while participating in local theatre productions. ==Career==