The first major career appointment that Tehmina Janjua had was from 1986 to 1987, as the desk officer to the Soviet Union and Eastern Europe in the Foreign Office.[6] In 1989, she served as the acting director of the Office of the National Security Adviser. Following her time at the Ministry of Foreign Affairs in Islamabad, Janjua completed her first mission abroad as the Second Secretary and then the First Secretary of the Permanent Mission of Pakistan to the United Nations, New York from 1990 to 1995.[7]
After returning to Pakistan for a year to serve as Director Foreign Secretary's Office, Janjua was posted to Geneva as Counsellor Pakistan Mission to the United Nations and Other International Organizations in 1996. During her time as Counsellor, she represented Pakistan at the Organization of Islamic Conference in March 1997, reiterating the importance of promoting a better image of Islam and Muslims.[8] The following year at a commission on human rights in April, on the topic of Kashmir she brought up the right to self-determination and the need for protecting individuals against human rights abuses.[9]
When her time as Counsellor in Geneva ended, she returned to Pakistan to serve as the Director Minister of State for Foreign Affairs' Office in 2000. A few years later, in 2004 she served as Director at the Foreign Secretary's Office.[10] In April 2004, while representing Pakistan in Geneva at the United Nations, Tehmina Janjua spoke in support of women’s rights, detailing Pakistan’s efforts to empower women politically and economically.[11] The following year, her experience was utilized as Deputy Permanent Representative of Pakistan to the United Nations and Other International Organizations, in Geneva until 2009.
From 2009 till 2011, Janjua served as the Director General of Strategic Planning in the Foreign Secretary's Office. After replacing Abdul Basit in February 2011, Janjua became the Spokesperson of the Ministry of Foreign Affairs of Pakistan.[12][13] As Spokesperson, Janjua provided important details of the safe return of Pakistanis from Libya, the on-going Indo-Pak talks and the drone strikes initiated by the United States during her term.[14][15][16]
She served as the Ambassador of Pakistan to Italy between December 2011 and October 2015.[17][18][19] On 6 October 2015, Janjua became Pakistan's envoy to the UN Office in Geneva. In December 2016, she became the first woman, and the first developing country representative, to preside over the Convention on Certain Conventional Weapons.[20]