All 189 people on board died when Flight JT610 fell into the sea shortly after taking off for the short journey to Pangkal Pinang.
The pilot had asked air traffic control for permission to turn back to the airport but then contact was lost.
Investigators say the plane had encountered technical problems.
The aircraft - a new Boeing 737 Max - broke into many pieces when it hit the water at high speed. The plane should not have been flying on the day it went down as it was not airworthy, Indonesian investigators have said.
The bright orange voice recorder was found at least 50m (165ft) from where the first black box - the plane's flight data recorder - was found last November.
The voice recorder was found on Monday morning but was "broken into two pieces".
Indonesia's Navy spokesman Agung Nugroho told Reuters that the recorder was found 8m deep, under mud on the sea floor.
Mr Nugroho said that a weak signal from the recorder had been detected "for several days".
He added that the recorder had "obvious scratches on it", but that it was unclear what damage it had suffered.
Human remains had also been found near where the voice recorder was discovered, said Mr Nugroho.
When the flight data recorder was found in November, officials said that it could take up to six months to analyse data.
Listening to the last conversations between the pilots and ground control on the CVR should help investigators finish piecing together what went wrong in the short flight.
Findings by Indonesia's transport safety committee (KNKT) suggest that Lion Air had put the plane back into service despite it having had problems on earlier flights.
The pilots appeared to struggle with an automated system designed to keep the plane from stalling - a new feature of the Boeing 737 Max.
The anti-stalling system repeatedly forced the plane's nose down, despite efforts by pilots to correct this, the findings suggest.
Investigators have now said that the plane was not airworthy and should have been grounded.
Some victims' families are suing Boeing over the accident.