Spalletti will reportedly be earning five million euros ($5.8 million) a season from his extended contract.
"We are delighted to have extended Luciano's contract for a further two seasons," said Juventus CEO Damien Comolli.
Spalletti was brought in by Juve in October to replace the sacked Igor Tudor and charged with ensuring qualification for the Champions League.
"It's important that I tell you first before it becomes official that we have decided to extend my contract for two more years," Spaletti said in a video released by Juve which showed him speaking to his players.
The club have been convinced by the 67-year-old who most famously won the Serie A title with Napoli in 2023.
"Since Luciano joined our great Juventus family, he has had an immediate and very positive impact on our players, the whole club and the entire Bianconeri community," Comolli said.
Spalletti, whose previous job was a tumultuous and unsuccessful stint as Italy coach, has Juve one point away from fourth place, which is currently occupied by Como.
However, the gap is effectively two points as Como won both meetings between the two teams this season.
Juve face another Champions League qualification contender in Atalanta on Saturday night.
