Terms were not immediately disclosed.
Selected 30th overall, Best is expected to share backfield duties with incumbent starter Kevin Smith, who continues to recover from an ACL injury suffered last year.
A sure-handed pass catcher and vibrant open field runner, Best's skills will be leveraged most on third-down situations and possibly in the return game.
When discussing the importance of quarterback Matt Stafford's new weaponry, Lions coach Jim Schwartz quipped during Friday's pre-camp briefing: "Adding Jahvid Best in there ... a guy who you can throw a three-yard pass to and can go the distance."
Lions Sign RB Jahvid Best.
The signing of Best still leaves his first round counterpart, and second overall selection Ndamukong Suh, without a contract.
Schwartz noted that Best was closer than Suh, primarily because top overall pick Sam Bradford and other early first rounders remained unsigned.
"Suh is a little different," conceded Schwartz. "When one domino falls you start getting a lot more (to fall). And I think the biggest domino in this draft is Sam Bradford at no. 1.
Added Schwartz, "Those two guys will be ready to go and will be on the field as soon as we can get them there."
Players must report between 2 and 6 p.m., EST, to the team's Allen Park training facility. They will begin conditioning drills and more over the weekend.
Getting amped for the 2010 regular season? Share your thoughts with other fans in The Den, the internet's most popular Detroit Lions forum! Go Now.