The assailants opened fired at Sena leader Mohan Raut at around 11.30 AM in Apte Wadi locality of Thane's Badlapur township.
Raut, in his late thirties, was rushed to Ulhasnagar Central Hospital where he was declared brought dead, police said.
The motive behind the killing was yet to be ascertained, police said, adding that it was immediately not known as to how many persons were involved in the killing.
Investigations were on into the murder, they added.