Jain, a 1992 batch Indian Revenue Service (IRS) officer, is at present serving as a Director in the Central Board of Direct Taxes (CBDT) under the Finance Ministry.
He will be "relieved of his duties" with effect from March 16 to take up the new assignment, a Finance Ministry order said.
Jain has been appointed as OSD to Kejriwal, who is also an ex-IRS officer, for a period of three years on deputation basis.