Sources told NFL Network, ESPN and The Athletic on Tuesday that Henry and the Patriots agreed to a three-year, $37.5 million contract. The deal includes $25 million guaranteed, but won't be official until the start of free agency at 4 p.m. EDT Wednesday.
The move to sign Henry comes just a day after the Patriots agreed to a four-year contract with former Tennessee Titans tight end Jonnu Smith.
The Patriots agreed to a two-year deal with former Las Vegas Raiders wide receiver Nelson Agholor and former San Francisco 49ers wide receiver Kendrick Bourne earlier this week.
Henry, 26, was a second-round pick in the 2016 NFL Draft. He has spent the last five seasons with the Los Angeles Chargers.
The 6-foot-5, 250-pound pass catcher had a career-high 60 catches for 613 yards and four touchdowns in 14 starts last season.