Vick can immediately participate in preseason practices, workouts and meetings and can play in the final two preseason games - if he can find a team that will sign him. A number of teams have already said they would not.
"Needless to say, your margin for error is extremely limited," Goodell said in a letter to Vick. "I urge you to take full advantage of the resources available to support you and to dedicate yourself to rebuilding your life and your career. If you do this, the NFL will support you."
Goodell suspended Vick indefinitely in August 2007 after the former Atlanta Falcons quarterback admitted bankrolling the "Bad Newz Kennels" dogfighting operation. Goodell said then that Vick must show remorse and signs that he has changed before he would consider reinstating him.
"I accept that you are sincere when you say that you want to, and will, turn your life around, and that you intend to be a positive role model for others," Goodell added. "I am prepared to offer you that opportunity. Whether you succeed is entirely in your hands."
Once the season begins, Vick may participate in all team activities except games, and Goodell said he would consider Vick for full reinstatement by Week 6 (Oct. 18-19).
Goodell called a news conference for late Monday afternoon.
"I would like to express my sincere gratitude and appreciation to commissioner Goodell for allowing me to be readmitted to the National Football League," Vick said through agent Joel Segal. "I fully understand that playing football in the NFL is a privilege, not a right, and I am truly thankful for the opportunity I have been given.
"As you can imagine, the last two years have given me time to re-evaluate my life, mature as an individual and fully understand the terrible mistakes I have made in the past and what type of life I must lead moving forward.
"Again, I want to thank the commissioner for the chance to return to the game I love and the opportunity to become an example of positive change."
The announcement came after a busy first week of freedom for Vick, who met with union leaders and Goodell on consecutive days last week. His 23-month federal sentence ended when an electronic monitor was removed from his ankle early on July 20 at his home in Hampton, Va.
He met with DeMaurice Smith, executive director of the NFL Players Association, last Tuesday and, on Wednesday, he sat down with Goodell at a security firm in Allendale, N.J.
But his issues are far from over. Already, the owners of the New York Giants and New York Jets said they have no interest in the 29-year-old quarterback, who once was the league's highest-paid player.
Vick needs to find a team so he can get himself out of financial ruin. He filed for bankruptcy protection last July, listing assets of about $16 million and debts of more than $20 million, and has a hearing about his plan to repay his creditors on Friday in Norfolk, Va. That plan is built around his ability to make NFL-type money again.
He's unlikely to command anything close to the 10-year, $130 million contract he once had with the Falcons, or to get endorsement deals after the grisly details of his involvement in the dogfighting ring.
Vick finally pleaded guilty after his three co-defendants had already done so. They told of how Vick participated in the killing of dogs that didn't perform well in test fights by shooting, hanging, drowning or slamming them to the ground.
Vick's appearances at federal court in Richmond, Va., all came with large groups of protestors outside. Many were with PETA and held signs depicting photographs of Pit Bulls ravaged in dogfights and decrying the brutality in the gruesome details that emerged in the case.
A smaller group came to show support for Vick wearing jerseys with his No. 7.
Vick has already taken some steps to begin rebuilding his image and showing remorse.
He met with the president of the Humane Society of the United States while serving the first 18 months of his federal sentence in the prison at Leavenworth, Kan. He plans to work with HSUS in a program designed to steer inner city youth away from dogfighting. He was not permitted to work with the program while in custody.
"It's been a long process," Segal said. "He's thrilled for the opportunity to resume his playing career. He understands he has a lot to prove."
Former coach Tony Dungy has agreed to continue his work with Vick as an advisor and mentor, according to Goodell.