Piquet said he was very disappointed with Renault's decision, but at the same time was relieved to put an end to "the worst period of my career."
"I can now move on and put my career back on the right track and try to recover my reputation of a fast, winning driver," Piquet Jr. said. "I am a team player and there are dozens of people I have worked with in my career who would vouch for my character and talent, except unfortunately the person that has had the most influence on my career in Formula 1."
Piquet said in a statement Monday that the "black period" of his career began when he signed a management contract with Briatore, who "threatened" him instead of supporting him. He called Briatore his "executioner."
"On numerous occasions, 15 minutes before qualifying and races, my manager and team boss would threaten me, telling me if I didn't get a good result, he had another driver ready to put in my place," Piquet Jr. said. "I have never needed threats before to get results."
The Brazilian driver's best finish in 28 races was second at the German Grand Prix in 2008. He earned 19 points and his highest starting position was seventh.
Piquet Jr., son of three-time world champion Nelson Piquet, said he decided to sign Briatore as his manager because he believed the experienced team principal was one of the best people to help him do well in F1.
"A manager is supposed to encourage you, support you, and provide you with opportunities," Piquet Jr. said. "In my case it was the opposite. Flavio Briatore was my executioner."
After a season as Renault's test driver, Piquet got a full ride for the 2008 season alongside two-time champion Fernando Alonzo. Piquet said some "strange situations began to happen" and that he never received "equal treatment."
"I was relegated as 'someone who drives the other car' with no attention at all," Piquet Jr. said. "The conditions I have had to deal with during the last two years have been very strange to say the least. There are incidents that I can hardly believe occurred myself."
The Brazilian driver said Briatore made him sign a performance-based contract which required him to score 40% of Alonso's points midway through the 2009 season.
"Despite driving with Fernando, two-time world champion and a really excellent driver, I was confident that, if I had the same conditions, I would easily attain the 40% of points required by the contract."
Piquet has not scored any points after 10 races this season, while Alonso has 13 points.
The Brazilian driver said he was not allowed to test as much as Alonso, and that the Spaniard was given a significant car upgrade in four of the first nine races this year.
"I was informed by the engineers at Renault that in those races I had a car that was between 0.5 seconds and 0.8 seconds a lap slower than my teammate," Piquet Jr. said.
He said he is already considering his options for a "new start" in his F1 career.
The Estado de S. Paulo newspaper in Brazil reported Monday that Nelson Piquet is negotiating to buy the BMW team in a partnership with Peter Sauber, a move which would secure a place for Piquet Jr. next year.