The BJP has been in power at the civic level since 2007.
The Centre on Friday appointed IAS officers Ashwani Kumar and Gyanesh Bharti as the Special Officer and Commissioner of the unified Municipal Corporation of Delhi (MCD), respectively, according to an order issued by the Ministry of Home Affairs.
Both the notifications will come into force from May 22 when the MCD will become a single entity.
"Now that appointment of special officer and commissioner has been done, the exercise of commissioning delimitation can be done," said a senior officer, adding the municipal elections can only be held after that.
Gyanesh Bharti is Commissioner of the unified Municipal Corporation of Delhi
As per State Election Commission delimitation exercise - which has been triggered by the reduction in the number of councillor seats - will take "at least a year".
"The encroachment drives will continue even after the merger," said an official.
The BJP-led civic bodies have launched an anti-encroachment drive which Chief Minister Arvind Kejriwal "biggest destruction" in Independent India.
The Act brings along a series of amendments that will limit the number of seats for councillors to not more than 250 - from the existing 272. Also, the word "Government" will be substituted with "Central Government" in 11 sections of the Delhi Municipal Corporation Act, 1957.
The Central government's proposal to merge the three corporations - which came to light on March 9, the day the State Election Commissioner was scheduled to announce the dates of civic polls in Delhi - triggered a war of words between the BJP and the Aam Aadmi Party.
While AAP said the BJP was "scared of holding municipal elections", Union Home Minister Amit Shah accused the Aam Aadmi Party government in Delhi of "stepmotherly treatment" towards the three civic bodies.
Mr Shah said two municipal corporations are in no state to sustain themselves financially, so they restructure taxes and tweak policies to continue operations.
The three municipal corporations were trifurcated in 2012 by the then Congress government in Delhi.
The Delhi Municipal Corporation (Amendment) Bill merged the North Delhi Municipal Corporation, the South Delhi Municipal Corporation, and the East Delhi Municipal Corporation.
The BJP has been in power at the civic level since 2007.