Razdan was administered the oath as UPSC chief by the outgoing chairperson D P Agrawal, whose tenure ended today.
Her new charge comes at a time when the Commission is facing a controversy due to the demand for change in the pattern of the examination from a section of aspirants.
The civil services preliminary examination is scheduled to be held on August 24.
She had joined as UPSC member on April 19, 2010.
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During her tenure as IAS officer, she had held several important assignments both in Haryana and at the Centre.
Her assignments at the Centre included Joint Secretary in the Ministry of Food, and Additional Secretary in the Ministry of Personnel, Public Grievances & Pensions.
In her home cadre, her assignments included Secretary, Cooperation and Public Health; Principal Secretary, Housing and Chairman, Haryana Housing Board. She has authored a number of publications.
The UPSC is headed by a chairman and 10 members.