[1][2] On 9 May 2009 Pope Benedict XVI appointed him Bishop of the Catholic Diocese of Embu.
As chairman, he oversaw the 58 hospitals, 83 health centers, 311 dispensaries, and 17 medical training institutions owned and operated by the Catholic Church in Keny'a.
At his installation ceremony he promised to "work together with all leaders in Wote Diocese to find solutions to pressing issues".
[7] In a 2024 book about plagiarism at the Gregorian University, researchers Michael Dougherty and Alkuin Schachenmayr argued that Njiru's dissertation was plagiarized, showing that very many passages were copied from uncredited authors like cardinals Leo Joseph Suenens and Albert Vanhoye.
The pope appointed Norman King'oo Wambua, Bishop of Machakos, as the Apostolic Administrator of the Diocese of Wote, with "full authority over all diocesan matters," effective 28 September 2024.