“The attack took place at his Dodoma residence at midday,” the main opposition party CHADEMA said in a statement, adding that Lissu was seriously wounded and rushed to hospital.
Party spokesperson Tumaini Makene described Lissu’s condition as “critical” while local media reported he had been shot in the stomach and leg.
Regional police commander Gilles Muroto said an investigation was underway.
“We are asking fellow citizens with information to help us,” he said, adding that initial enquiries were focussing on a car believed to have followed Lissu to his home.
Lissu, 49, has had a series of run-ins with the government of President John Magufuli and has been arrested at least six times this year, accused of insulting the president and disturbing public order among other charges.
Lissu serves as chief whip for the parliamentary opposition and president of Tanzania’s bar association, the Tanganyika Law Society, as well as being CHADEMA’s attorney general.
He was last arrested in August after revealing that a plane bought for the national carrier had been impounded in Canada over unpaid debts.
Magufuli has been praised for cracking down on corruption since 2015 but criticised for his authoritarian rule with opposition meetings banned and newspapers shut down, moves Lissu has loudly condemned as creating a “climate of fear”.
His party said Lissu was shot just after a parliamentary session.
“CHADEMA strongly condemns this act, and we are following up closely on his situation,” the party added.