Chief Justice Nasirul Mulk administered the oath of office to Justice Raza.
Earlier on Thursday, the parliamentary committee for the appointment of CEC had agreed on the name of Justice Sardar Mohammad Raza Khan as the new CEC.
Born in 1945 in Namli Maira in Abbottabad district, Khan has an MA in economics and an LLB degree from Punjab University.
He became a civil judge in 1968 and fast earned the reputation of one unwilling to budge from his principles. Khan became an additional judge for two years in 1993 and before taking permanent office at the Peshawar High Court.
He was appointed chief justice of the Peshawar High Court in 2000 by Mohammad Rafiq Tarar and two years later became a judge at the Supreme Court. After refusing to take oath under the Provisional Constitutional Order (PCO) on Nov 3, 2007, he was removed from the Supreme Court after the imposition of emergency by then military ruler Pervez Musharraf. He was reinstated to the court under the democratically-elected government which came to power in 2008.
He retired from the Supreme Court of Pakistan in 2010.
Khan has served as the acting Chief Justice of Pakistan in addition to twice taking up the post of the acting governor of Khyber Pakhtunkhwa. He has also filled the role of interim chief CEC.
Justice Sardar resigned as chief justice of the Federal Shariat Court on Friday, a post he had to relinquish with his appointment as the new CEC.
He assumes the charge at a time when the ECP is under pressure to hold local government elections across the country, particularly in Punjab and Sindh, without any further delays, even as provincial governments continue to drag their feet.