Born in South Africa, Coatsworth moved to New Zealand when she was eight. She works as a child psychologist and owns a small farm in the Coromandel. Coatsworth joined the Labour Party in the 1980s during anti-mining campaigns in the Coromandel.
Before being elected President, Coatsworth was Senior Vice President of the Labour Party.
She was elected President of the Labour Party unopposed on 2 April 2011. She has "absolutely no ambition" to be an Member of Parliament.
On 26 November 2014, Coatsworth announced her intention to move forward her resignation as President to mid-December 2014, after completing the election in which Andrew Little was elected Party Leader, and starting the party"s 2014 review.
She stated that her reasons for leaving were that she wants "to see a new president working with Andrew as the new leader, really hitting the ground running at the beginning of next year and getting a plan in and getting moving." Nigel Haworth was elected as her successor.