The draft law, which has been presented to the cabinet for approval, also awards him a lifetime salary.
It also proposes that Mr Nkurunziza be elevated to the title of "supreme leader" when he steps down in May.
Burundi was plunged into a constitutional crisis in 2015 when he successfully ran for a third term.
The move sparked violent protests by opposition supporters which morphed into reprisal attacks.
Last year a UN commission accused the government of human rights abuses, including executions, arbitrary arrests, torture and sexual violence.
Burundi called the claims "lies".
Last year, Burundi banned the BBC from operating in the country, accusing it of producing a documentary that had damaged the country's reputation.