The NFL announced Wednesday that arbitrator Harold Henderson upheld the suspension for a failed test for marijuana. The Pro Bowler had appealed the ruling and met with Henderson and other league officials in New York on Aug. 4.
Gordon's suspension is effective immediately, and the league said in its statement that his "eligibility for reinstatement will be determined following the 2014 season." Gordon does remain under the care of medical professionals in the NFL treatment program, which includes counseling and rehab, if necessary. He also remains subject to random testing.
In the meantime, Gordon is not allowed to practice with the Browns, attend team meetings or other club functions.
Gordon served a two-game suspension for a drug violation last season but still led the league in yards receiving and emerged as one of the game's top players.
"I'd like to apologize to my teammates, coaches, the Cleveland Browns organization and our fans," Gordon said in a statement released by the NFL Players Association. "I am very disappointed that the NFL and its hearing office didn't exercise better discretion and judgment in my case. I would like to sincerely thank the people who have been incredibly supportive of me during this challenging time, including my family, my agent, my union, my legal team, and the Cleveland Browns staff."
The Browns have been waiting four months for a resolution to Gordon's case, which hung over him and the team. He continued to practice and played in Cleveland's first three exhibition games.
The Browns have been baffled as to why it has taken so long for the league to rule on the appeal and have been increasingly frustrated over where the suspension would leave them and Gordon, team sources told ESPN NFL Insider Adam Schefter.
"While we may have strong feelings on the timing and the process of this decision, we have also consistently communicated that we will focus on what we can control in our day to day approach," general manager Ray Farmer said in a statement. "Right now that is preparing our team for the 2014 season and at the same time, supporting Josh however we are able under NFL guidelines during his suspension."
Gordon fought the suspension, hiring attorney Maurice Suh to represent him at the appeal hearing.
Suh, who had successfully gotten a suspension reduced for Seattle cornerback Richard Sherman, argued that Gordon tested positive for marijuana due to secondhand smoke, sources told ESPN last month. Gordon's representatives also said test results of his samples were inconsistent and should be thrown out.
There was speculation that the NFL might go softer on Gordon following the public outcry after Baltimore running back Ray Rice was suspended for two games on a domestic violence charge. Instead, the league is putting Gordon on the sideline for all 16 games and will wait to see how he behaves before deciding whether to let him play again.
Gordon didn't help his cause with two legal issues as his case dragged on. He was charged with drunken driving after his arrest in Raleigh, North Carolina, on July 5. In May, he was stopped for speeding in Strongsville, Ohio, and one of the passengers in his car was cited for marijuana possession.
Gordon's loss is a crippling blow to Cleveland's offense, depriving the Browns of their best big-play threat. He averaged 18.9 yards per catch in 2013 and became the first player in league history to record consecutive 200-yard games.
The talented 23-year-old set the Browns' single-season franchise record with a league-leading 1,646 receiving yards last year despite the two-game suspension. It was his second known violation, but Gordon said he had inadvertently taken codeine contained in a prescription cough syrup. The breakout performance included one dazzling four-game stretch where Gordon had 36 receptions for 774 yards and five touchdowns.
"We will continue to support Josh and we understand that there is accountability for one's actions," coach Mike Pettine said in a statement. "Our job and that of the team is to focus on what we can control. Our philosophy in building this team and the mentality we're establishing is that we're going to have to overcome challenges and situations throughout the course of a season. We'll continue to be relentless in our approach, in how we work and focus on our goal of returning winning football to Cleveland."
The Browns took a risk in selecting Gordon in the 2012 supplemental draft, forfeiting a second-round pick to take the speedy 6-foot-3, 225-pounder who failed at least three drug tests in college for marijuana abuse.
The team has vowed to do all it can to help and support Gordon, who recently posted a photo on Instagram of him catching a pass from rookie quarterback Johnny Manziel. Gordon captioned the photo, "Only place I can find peace."
ESPN NFL Insider Adam Schefter, ESPN Senior NFL Analyst Chris Mortensen, ESPN.com Browns reporter Pat McManamon and The Associated Press contributed to this report.