Sharma, a three-time legislator and Rajya Sabha member, is a legislator from Mandi.
There is still one vacancy in the cabinet. Singh has said the next expansion would be after the state's budget session beginning Mar 12.
Official sources said in the next expansion the chief minister is keen to induct four to five legislators as chief parliamentary secretaries.
Singh, who had been chief minister in 1983, 1985, 1993, 1998 and 2003, took the oath of office for thee sixth time December 25, 2012, with his nine cabinet colleagues.
The Congress won a majority with 36 seats in the 68-member assembly.