Prior to this tenure, she was Mexico's Permanent Representative to the United Nations in Geneva.

She started her diplomatic career in 1992 when she joined the Ministry of Foreign Relations and rose through the ranks to the position of Director of International Law in the Legal Consultancy and Coordinator of Advisors in the Undersecretariat for Multilateral Affairs and Human Rights.

[3] As a diplomat, she was in charge of the Mexican delegation involved in the negotiations which lead to the Rome Statute in 1998[1] and in consequence to the establishment of the International Criminal Court.

In 2017, she was appointed Mexico's Permanent Representative to the United Nations in Geneva, Switzerland.

[4] She was elected Judge of the International Criminal Court by the Assembly of States Parties to the ICC following the Court's Independent Expert Report which showed that Liera received the highest rating and the highest number of votes among 18 contenders.