She is Canada's first Ambassador for Women, Peace and Security, and a co-founder of the Roméo Dallaire Child Soldiers Initiative.

[2] From 2011, O'Neill worked as a federal government adviser on advancing peace and security for women.

[3] She has previously worked for NATO, the Organization for Security and Co-operation in Europe, and the United Nations.

[5][6] O’Neill has been Global Fellow at the Woodrow Wilson International Center for Scholars, an adjunct professor at Georgetown University, and has served on the board of directors of the Canadian International Council.

[6] In June 2019, O'Neill was appointed as Canada's first ambassador for women, peace and security.