The opposition has accused Mr Chawla of favouring the ruling Congress
A controversial new chief election commissioner is to take office in India four days after the start of the marathon five-phase general election.
Navin Chawla will take over from N Gopalaswami, who had urged his rival's removal from the commission for favouring the ruling Congress party.
The government said Mr Gopalaswami's demand had no merit.
The Election Commission is an autonomous, three-member body aimed at delivering free and fair elections.
Mr Gopalaswami's term as commission head was always scheduled to end on 20 April.
Mr Chawla will take over as chief commissioner and V S Sampath will be promoted to the three-member body to join current commissioner SY Quraishi.
Mr Chawla will serve as commission head until 29 July 2010.
Mr Gopalaswami maintained his rivalry with Mr Chawla to the end
In January, Mr Gopalaswami petitioned India's president to remove Mr Chawla, accusing him of "bias".
At the time India's Law Minister Hans Raj Bharadwaj said Mr Gopalaswami "should do his work in the EC [Election Commission] and not become a political boss".
The opposition Bharatiya Janata Party has also accused Mr Chawla of favouring Congress and last year lodged a complaint with Mr Gopalaswami.
Congress criticised the BJP for an "irresponsible and short-sighted assault" on the commission.
Mr Chawla and Mr Gopalaswami maintained their rivalry to the end.
On Sunday Mr Gopalaswami was the dissenting voice in a split 2-1 decision which ruled that Congress president Sonia Gandhi should not be stripped of her membership of the lower house of parliament for accepting a foreign award.
A petition had been brought by a lawyer claiming Sonia Gandhi should be disqualified as the constitution demands that an MP cannot be "under any acknowledgment of allegiance or adherence to a foreign state".
Mr Chawla also faces controversy over the arrest of BJP politician Ashok Sahu.
The Election Commission last week ordered his arrest in connection with an alleged hate speech against Christians in the eastern state of Orissa.
Mr Sahu accused Mr Chawla of behaving in a "partisan manner".
"The EC is not above the law. He derives his powers from the law and should function within its ambit," Mr Sahu said.
Mr Chawla will oversee the final four phases of the election, with final voting on 13 May and counting on 16 May.