Ms Lankesh, who ran her own Kannada publication, was shot dead by unidentified assailants at her residence in Bengaluru.
"The truth will never be silenced. Gauri Lankesh lives on in our hearts. My condolences and love to her family. The culprits have to be punished," he said on Twitter.
The truth will never be silenced. Gauri Lankesh lives on in our hearts. My condolences &love to her family. The culprits have to be punishedOffice of RG (@OfficeOfRG) September 5, 2017
Congress leader Kapil Sibal tweeted, "Gauri a rationalist silenced by gunshots. Her murder is an attempt to stifle reason, to silence those holding contrarian views. Tragic."
She took more than one bullet and died instantaneously. Ms Lankesh, said to be in her 50s, edited a Kannada tabloid 'Lankesh Patrike' besides owning some other publications, and was known for her forthright views against hardline Hindutva politics.