He became the second major offensive addition by the Patriots on Monday. Tight end Jonnu Smith agreed to a four-year, $50 million contract, including $31.25 million guaranteed, agent Drew Rosenhaus told Schefter.
The Patriots also have spent big on the defensive side, adding pass-rusher Matthew Judon on a four-year, $56 million deal, including $32 million guaranteed, sources told Schefter.
Agholor, signed by the Raiders to a one-year, $1,047,500 million prove-it deal last March after essentially being run out of Philadelphia because of the former first-round pick's proclivity for drops, reinvented himself last season in Las Vegas.
He was the most efficient wideout on the Raiders' roster, scoring a touchdown in eight of the Raiders' 16 games. The eight touchdown catches tied his career high, and they included six of at least 20 yards -- which ranked second in the league.
Agholor, the 20th overall pick of the 2015 draft, finished last season with a career-high 896 yards on 48 catches for a career-best 18.7 yards-per-catch average, which ranked second among NFL players with at least 25 receptions.
Raiders quarterback Derek Carr had a 100.5 passer rating when targeting Agholor, who also had 15 catches of at least 20 yards, which ranked 19th in the NFL.
Agholor, who turns 28 on May 24, was signed more for depth but ended up filling a need at the position when deep-threat Tyrell Williams was lost for the season in training camp with a shoulder injury and speedsters Henry Ruggs III and Bryan Edwards hit the rookie wall. His biggest game came in a losing effort to the Miami Dolphins in Week 16, when he had a career-high 155 yards receiving, including a career-long 85-yard TD. Zebra Technologies Next Gen Stats had Agholor going 117.8 yards of total distance on that score, the most yards traveled on an offensive scoring play through that point of the season.
In six seasons, he has 272 catches for 3,411 yards and 26 touchdowns.
The Patriots also agreed to a 3-year, $22.5 million deal with wide receiver Kendrick Bourne, a source told Schefter. Bourne, 25, had 667 yards and two touchdowns with the San Francisco 49ers last season.
ESPN's Paul Gutierrez contributed to this report.