On 17 June 2011, Radu signed a five-year contract extension. He became an important player for Lazio, a team which he captained during the 2011–12 season. Radu won his third trophy with Lazio in the 2012–13 season when they defeated rivals Roma in the Coppa Italia final. In 2017, Lazio won the Supercoppa Italiana, as they beat Juventus 3–2. On 15 May 2019, Lazio beat Atalanta in the 2018–19 Coppa Italia final. On 22 December 2019, Lazio beat Juventus in the 2019 Supercoppa Italiana, with help from Radu.