An official announcement is not expected until Thursday, a source told ESPN.
Sources told ESPN that Del Rio interviewed Tuesday night with owner Mark Davis, general manager Reggie McKenzie and former Raiders coach John Madden, the Hall of Famer who has been a proponent of Del Rio.
The other finalist for the job was Tony Sparano, who was the interim coach for the final 12 games of the season.
The Raiders also interviewed former Jets and Browns coach Eric Mangini, Eagles offensive coordinator Pat Shurmur, Colts offensive coordinator Pep Hamilton, Seahawks offensive coordinator Darrell Bevell and former Broncos and Redskins coach Mike Shanahan, who was fired as Raiders coach by the late Al Davis four games into the 1989 season after the team started 1-3.
Del Rio has reached out to former Chicago Bears coach Marc Trestman about joining the team as offensive coordinator, a source told ESPN.com.
Broncos defensive tackle Terrance Knighton endorsed Del Rio on Twitter.
If the report is true. The Raiders are getting a great damn coach. He will revive that locker room and organization.
— Terrance Knighton (@MrKnighton2u) January 14, 2015
Del Rio coached the Jacksonville Jaguars from 2003 to 2011, compiling a 68-71 record while twice guiding the team to the playoffs. He also served as interim coach of the Broncos in 2013 when then-head coach John Fox had health issues.
Del Rio, who initially met with Mark Davis on Jan. 4, grew up in the East Bay Area, and his family is longtime Raiders season-ticket holders.
The Hayward, California, native, was hired by the Broncos after Dennis Allen left the team following the 2011 season to become the Raiders' head coach. Del Rio, if hired in Oakland, would be replacing Allen, who was fired earlier this season.
The Broncos finished No. 3 in total defense this season and led the league in forcing three-and-outs. In 2012, Del Rio's first season in Denver, the Broncos were No. 2 in overall defense, No. 4 in scoring defense and tied for the league lead in sacks.
Oakland has had eight coaches since the start of the 2003 season. The Raiders have not had a winning record or playoff berth in that span as the constant turnover has contributed to the struggles on the field.
Sparano, who went 3-9 in place of Allen, was formerly the head coach in Miami.
The Raiders have hired only three coaches -- Joe Bugel, Norv Turner and Art Shell in his second stint -- who had previously been head coaches on professional teams, as Al Davis often preferred young up-and-comers over retreads.
Jeff Legwold, Bill Williamson and Jeremy Fowler of ESPN.com, ESPN NFL Insider Adam Schefter and The Associated Press contributed to this report.