Authority

The PSC is an Independent Commission whose existence and authority are firmly anchored in the New Constitution. Excerpts from Chapter 13 - The Public Service, Part 2 - The Public Service Commission, Article 233:

233. (1) There is established the Public Service Commission.

248. (2) The commissions are—  (g) the Public Service Commission;

The PSC has assumed some of the powers the President had under the Old Constitution such as the design and establishment of departments and offices, as well as the authority to hire persons for top positions within the Civil Service (as the Public Service was then known). Excerpts from Chapter 9 - The Executive, Part 2 - The President and Deputy President:

132. (4) The President may— (a) perform any other executive function provided for in this Constitution or in national legislation and, except as otherwise provided for in this Constitution, may establish an office in the public service in accordance with the recommendation of the Public Service Commission;

And from Part 3 - The Cabinet, in Chapter 9:

155. (3) The President shall— (a) nominate a person for appointment as Principal Secretary from among persons recommended by the Public Service Commission; .......

The two preceding excerpts above from Articles 132 and 155 are designed to take away from the President, the often-abused powers of appointment to high office. Indeed, the PSC conducted the (public) recruitment and shortlisting of persons from whom the President chose his nominees for Principal Secretary. This move (and others) ensure that the PSC like other Commissions protects the rights and liberties of the people of Kenya guaranteed by Article 249 i.e., 249. (1) ...... to— (a) protect the sovereignty of the people; (b) secure the observance by all State organs of democratic values and principles; and (c) promote constitutionalism.

The Commission has the mandate to setup the Public Service bureaucracy and to fill positions within it:

234. (2) The Commission shall— (a) ....... (i) establish and abolish offices in the public service; and (ii) appoint persons to hold or act in those offices, and  to confirm appointments; 

Indeed, in November 2013, the Cabinet Secretary for Lands, Housing and Urban Development had to withdraw a gazette notice in which she had purported to establish the office of a Director-General for Lands in place of the soon-to-be phased-out-position of the Commissioner for Lands - a move that was clearly in contravention of the Constitution's mandate that the PSC is the body vested with the authority to create such an office. 

The PSC is also responsible for the hiring and discipline of staff working in the Service:

234. (2) The Commission shall— (b) exercise disciplinary control over and remove persons holding or acting in those offices;

The PSC will have powers to receive and consider a petition from a citizen seeking the removal of the Director of Public Prosecution and to advise the President during the life of the petition:

158. (2) A person desiring the removal of the Director of Public Prosecutions may present a petition to the Public Service Commission .......
(3) The Public Service Commission shall consider the petition and, if it is satisfied that it discloses the existence of a ground, ...... it shall send the petition to the President.
(4) On receipt and examination of the petition, the President shall, ......, acting in accordance with the advice of the Public Service Commission, appoint a tribunal .......