Njue was born in Embu, Kenya, on 1 January 1946[a] to Joseph Nyanga Kibariki and Monica Ngina Nyaga.

He received his episcopal consecration on the following 20 September from Jozef Cardinal Tomko, the co-consecrators being Bishops Silas Silvius Njiru and Raphael Ndingi Mwana'a Nzeki.

Shortly afterwards, he was created Cardinal-Priest of Preziosissimo Sangue di Nostro Signore Gesù Cristo by Pope Benedict XVI in the consistory of 24 November 2007.

On 28 March 2013, he appealed for calm and peace during the upcoming Easter season as the Supreme Court of Kenya prepared to announce its verdict in the disputed initial round of the presidential election held on 4 March between Uhuru Kenyatta and Kenya's Prime Minister Raila Odinga.

Kenyatta and Deputy President-elect William Ruto were facing charges at the International Criminal Court (ICC) at The Hague that they instigated post-electoral violence in Kenya after the 2007 election.

[9] A few weeks later, the Apostolic Nuncio to Kenya, Archbishop Charles Daniel Balvo, alongside Bishop Paul Kariuki Njiru of Embu, told a Catholic assembly that "The homosexuals should be defended against violation of their dignity and human rights, they are human beings like anyone of us.

"[10] In March 2014, Njue advised against participation in a free government program to vaccinate women of reproductive age against tetanus.