The New York Jets released Harris on June 6 after being unable to agree on a pay cut with the linebacker, who played 10 seasons for the team.
In reaching an agreement with Harris, the Patriots could have answered one of their few roster-related questions entering training camp: Who plays the most snaps alongside Dont'a Hightower?
Elandon Roberts, Shea McClellin and Kyle Van Noy were top candidates before the addition of Harris. All should still play notable roles in various sub packages, as the team tailors its game plans each week, with Harris now arguably the leading candidate for most snaps alongside Hightower.
Harris, 33, the Jets' longest-tenured player, was blindsided by his Jets release. He had practiced earlier in the day in his usual spot at starting middle linebacker and later talked with ESPN about his longevity as the only holdover from the Eric Mangini era (2006 to 2008).
A second-round pick in 2007, Harris ranks No. 2 in tackles in Jets team history. He called the signals for Jets coach Todd Bowles' defense and played 87 percent of the defensive snaps in 2016.
Harris, who was known for his durability, started and played in 137 of the past 138 games. He missed one game last season, snapping a streak of 121 starts.
ESPN's Mike Reiss and Rich Cimini contributed to this report.