The IRS officer posted in Faridabad thought her friends were pulling her leg.
Haritha V Kumar, who emerged topper in the All-India Civil Services Examination, initially did not believe it was true as she thought her friends had played a prank.
"Initially, I could not believe it was true. I thought I was being fooled by my friends who called me over phone to congratulate," Haritha told a Malayalam TV channel from Faridabad.
Haritha, who is already an officer in the Indian Revenue Service (IRS) and posted at Faridabad, clinched the top rank in the civil service in her fourth attempt.
"I thank my teachers, well-wishers and friends for my success," said Haritha, who hails from Kerala's capital of Thiruvanathapuram.
"This victory is the result of her hard work, dedication and determination. We thank God and all those who have helped her," Haritha's parents said.
An engineering graduate, Haritha chose economics and Malayalam as her main subjects for the civil service.
It is after two decades that a candidate from Kerala has emerged topper in the All-India Civil Services Examination.
V Sriram from Kochi secured the second rank and Albi John Verghese from Muvvattupuzha got the fourth rank in the examination held in 2012.