Rădoi started to play football at the age of eight, first as a goalkeeper and then as a defender. He started his youth career at Turnu Severin and there he was spotted by Sorin Cârțu, the coach of Extensiv Craiova, whi was so impressed by Radoi that he purchased Rădoi in 1999, financing the transfer with his own money. Rădoi made his professional debut in 1999, in a defeat against Dinamo București on 4 March 2000. he left the club.
Steaua București
Just one year later, in the summer of 2000, Rădoi joined FC Steaua București for a fee of €110,000. Describing his first day at Steaua, he said, "It was like a positive shock for me. Suddenly I was in the same place with players like Iulian Miu, Marius Baciu and Miodrag Belodedici, players I saw on TV. It was like a dream." His coach at Steaua was Victor Pițurcă, the former Romania national team coach, who promoted him to the Steaua first team. He then became one of Steaua's most important players. In his first match for the club, a 4-3 victory over FCM Bacău at the Ghencea football stadium, Rădoi scored the equalizer in the ninth minute after Cătălin Cursaru had opened the scoring for Bacău less than a minute before. Steaua would go on to win the championship of the Romanian league that year, as well as the Supercupa României against rivals Dinamo. In 2005, Rădoi won a second championship title; and in 2006, yet another: his third, and Steaua's 23rd. On 24 February 2005, he won an important match in the UEFA Cup against holder Valencia. In 2006 Rădoi captained the team in the UEFA Cup semi-final against Middlesbrough which Steaua lost 4–3 on aggregate. In 2006, after a ten-year absence, Steaua qualified for the UEFA Champions League, grouped with Real Madrid, Lyon and Dynamo Kyiv, although Rădoi did not play in the first games due to injury. In the summer of 2006, a rumour circulated that Rădoi would sign for Premier League club Portsmouth as soon as the transfer window opened in England, with the transfer fee estimated at around £11 million. The transfer did not materialize, however, and many speculated that the £11 million offer was no more than a ploy to jack up the player's potential transfer value before a move elsewhere. In the end, Steaua owner Gigi Becali stated that he would not be selling Rădoi after all. Due to injury, he only played his first official game in the 2006–07 season on 12 November, a 6–0 victory against Național București. He was a key player for Steaua in his nine seasons and captained the team for several years.
Later career
In January 2009, Rădoi signed a three-year contract with Saudi Arabian club Al-Hilal which earned him €1.4 million annually. The transfer fee Steaua received was in the region of €6 million. Rădoi made his debut for Al-Hilal in the local derby against Al-Nassr, which Al-Hilal won 2–0 with Rădoi scoring the second goal. In his sixth game with the club, he won the Prince's Cup, defeating Al-Shabab in the final. Nicknamed "The Warrior" by his fans in Saudi Arabia, he was voted Saudi Professional LeaguePlayer of the Year in 2010. They even made a complete book about his career and has been published online with official website MRadoi.com. Rădoi spent three years at the club, becoming a legend, and the team's captain, before he was reunited with ex-Al-Hilal and Steaua manager Cosmin Olăroiu at Al Ain. In June 2011, Rădoi was transferred to Al Ain for a fee of €4.2 million. He signed a two-year deal worth €2.5 million annually.
International
Rădoi has been capped 67 times for the Romania, scoring two goals. In 2005, Romanian team manager Victor Pițurcă suspended him for leaving training campwithout permission before matches against the Netherlands and Armenia. Coach Pițurcă recalled him in February 2006 for a friendly tournament in Cyprus after Rădoi apologised for his behaviour. Although he was included in Romania's squad for UEFA Euro 2008, he suffered an eye injury and broken nose during the second group game against Italy after clashing heads with team-mate Răzvan Raț, who emerged unscathed. Rădoi played no further part in the tournament. After a confrontation with Răzvan Lucescu in 2010, Radoi declared that he would retire from the national team.