Ellison was elected at the 2010 general election, with a majority of 5,977.[8] In Parliament, she served on the Backbench Business Committee and Work and Pensions Committee.[8] In 2011 she founded the first All Party Parliamentary Group on Female Genital Mutilation (FGM),[9] speaking regularly on the issue in Parliament.
Ellison was appointed Parliamentary Under-Secretary of State for Public Health in October 2013.[6][8] She continued her interest in FGM, bringing forward a number of measures aimed at ending the practise during her time as a Minister.[10][11] She described providing political direction to the National Health Service (NHS) as "a bit like being on a high wire without a net at times, it can be quite exciting" in a meeting with the Tory Reform Group in 2014.[12]
According to The Observer, she also said: "I don't know how much any of you realise that with the Lansley act we pretty much gave away control of the NHS… we have some important strategic mechanisms but we don't really have day-to-day control", which was seized upon by critics as evidence that the government's NHS reforms had not succeeded.[12]
In January 2015, Ellison announced the government was proposing introducing a ban on advertising on cigarette packaging before the next election, and the standardised packaging of cigarettes legislation passed the House of Commons in March 2015.[13] After a Parliamentary debate in February 2015,[14] Ellison signed the Mitochondrial Donation Regulations on 4 March making the UK the first country in the world to legislate for the procedure.[15]
Following the EU Referendum in which she campaigned for Remain [16] Ellison was appointed Financial Secretary to the Treasury in July 2016[17] and in August 2016 she announced that the Government would be proceeding with the Soft Drinks Industry Levy, also known as the sugar tax.[18]
After politics
In October 2017 Ellison was appointed as Deputy Director-General for Corporate Operations at the World Health Organization under the leadership of Director GeneralTedros Adhanom Ghebreyesus. On 6 March 2019 as part of a wider programme of reorganization she became the Executive Director for External Relations and Governance at WHO.[19] She left the WHO in November 2022 when there were a number of changes in the senior leadership team.[20]