[2][3] Nkaissery was elected to the National Assembly in 2007 and served as an Assistant Minister for Internal Security in the cabinet of President Mwai Kibaki from 2008 to 2013.
When Operation Linda Nchi was launched in 2011, he served as the assistant minister to the Kenyan Ministry of Defence.
[4] On 2 December 2014, Nkaissery was nominated by President Uhuru Kenyatta for the post of Cabinet Secretary for Internal Security, to replace Joseph Ole Lenku, and subject to approval by the Parliament of Kenya.
Following his approval as Cabinet Secretary, Nkaissery stepped down as Member of Parliament for Kajiado Central Constituency.
He was pronounced dead in the morning on 8 July 2017, with post-mortem results showing that he had suffered from an acute myocardial Infarction.