Kailash Sankla was also chosen unopposed as the deputy mayor as no other party had filed nominations for the two posts.
While Ms Sehrawat represents Dwarka-B ward, Mr Sankla won from Punjabi Bagh in the high-stakes MCD polls held on April 23.
She had trounced AAP's Sushma Bansal in Dwarka-B ward by a record margin of 9,866 votes, the highest in the entire polls. Ms Sehrawat polled 14,613 while Ms Bansal could just get 4,747 votes.
The post of mayor sees five single-year term on a rotation basis, with the first year being reserved for women, the second for open category, third for reserved category, and the remaining two also being in the open category.
Members to the South Delhi Municipal Corporation's Standing Committee were also elected.
From the BJP, Bhupender Gupta was elected to the post of chairman, while Shikha Rai, Nandani Sharma and Tulsi Joshi were also elected. Poorva had withdrawn her nomination.
Congress' Andrews Ganj councillor Abhishek Dutt and AAP councillor from Hastsal ward, Ashok Kumar, were also elected.
Last year, Janakpuri councillor Shyam Sharma of the BJP was elected as mayor after defeating Praveen Rana of the Congress by a margin of 25 votes. Sharma had secured 62 votes out of total 99 valid votes polled.
The erstwhile unified Municipal Corporation of Delhi was trifurcated in 2012 into the NDMC, the SDMC and the EDMC. The first MCD poll after the trifurcation was held the same year.
The BJP had bagged 181 of the 270 wards in the civic polls. Delhi has a total of 272 wards.
While election to Maujpur ward in east Delhi was held on May 14, Sarai Pipal in north Delhi will go to polls on May 21.
Elections in these two wards were postponed due to death of candidates.
The BJP has been ruling the MCD for the last 10 years and yesterday Preeti Aggarwal was elected unopposed as the mayor of north Delhi amid an uproar in the NDMC House.