That means Thurman will miss a second straight season, putting his career in jeopardy.
NFL commissioner Roger Goodell, who met recently with Thurman, made the decision. The Bengals, who anticipated that Thurman would be cleared to return, made the announcement of Goodell's ruling on Thursday morning in a news release.
Thurman will be able to apply again for reinstatement after this season.
"I thought he was going to be reinstated, and if that's the direction the league is going to take, that's pretty hard-core," defensive end Justin Smith said, after reporting for training camp in Georgetown, Ky.
One of Thurman's representatives, Saf Lawson, had said repeatedly that his client was in compliance with the conditions of his one-year suspension, and that he expected to be back with the Bengals. Neither Thurman nor Lawson could be reached on Thursday morning for comment.
Thurman filed his reinstatement paperwork nearly a month ago, so that it would be in the NFL offices well in advance of July 12, which marked the one-year mark of his suspension.
Thurman, a Bengals' starter in 2005 when he led them in tackles as a rookie, was initially suspended for four games when he missed a scheduled drug screening. The sanction was subsequently increased to a year after Thurman was arrested on DUI charges Sept. 25.
Earlier this spring, Bengals coach Marvin Lewis indicated that Thurman would be welcomed back to the team, and would be able compete for a roster spot in training camp, if the league reinstated him.
"I have been in contact with Odell and he has an opportunity to be reinstated," Lewis said in mid-May, while appearing on a local radio show. "He will have had to ... [follow] the very strict NFL guidelines to get to that point and then, obviously, if reinstated, to go forward. And if that happens, he'll have an opportunity [to return]."
Lewis later backed away from that sentiment a bit and has not discussed Thurman's status in detail since then.
"I'm disappointed for Odell, but it is part of life," Lewis said.
At a media luncheon on Tuesday, owner Mike Brown supported Thurman.
"Odell has been through a difficult time," Brown said. "He's worked hard to bring himself back. It's the call of the league [about reinstatement]. I know one thing: If he can get back, he's a good player."
Last month, two men in Thurman's hometown of Monticello, Ga., filed complaints against Thurman, alleging that he hit and kicked them at a party. On the day the complaints were to be heard by a local magistrate, they were withdrawn. It is not known how that incident might have affected Goodell's decision to deny reinstatement.
Despite missing much of his rookie training camp because of a protracted contract impasse, the 24-year-old Thurman appeared in 15 games in 2005, all as a starter, and registered 148 tackles, one sack, five interceptions, nine passes defensed and four forced fumbles. The former University of Georgia star, a second-round draft pick in 2005, was a candidate for defensive rookie of the year honors.
"Aside from football, we just hope he gets himself better and gets himself out of trouble," quarterback Carson Palmer said. "Whether it's the football field, an office or whatever his future may hold for him, we just hope the best for him."
Len Pasquarelli is a senior NFL writer for ESPN.com. Information from The Associated Press was used in this report.