Pramod Mahajan, general secretary of theBharatiya Janata Party (BJP), was shot three times in the stomach and chest, the Press Trust of India (PTI) reported.
A N Roy, Bombay's police commissioner said, Mahajan was shot at point-blank range and underwent surgery on Saturday morning in Mumbai's Hinduja Hospital.
He was then put on respirator in intensive care where his condition was described as critical.
The shooting occured in Mahajan's 15th floor apartment in an upscale Mumbai neighbourhood.
Several other Indian politicians live in the same complex.
Pravin Mahajan, Pramod's younger brother, turned himself over to police immediately after the shooting.
He has since been charged with attempted murder, which carries a maximum sentence of life in jail.
The motive for the shooting was unclear.
A report from PTI quoting police sources said the shooting was the result of a property dispute between the two brothers.
However, Pravin's lawyer, told NDTV television hsi client had been suffering from "some mental disorder" in recent months.
He is "completely under depression, under mental trauma," Nandkumar Rajukar said.
"He is not in a position to speak properly or tell exactly what exactly happened."