Steaua București
On 17 June 2010 he was transferred to Steaua București. On 16 August 2010 Gardoș made his team debut for Steaua in Liga I against Victoria Brănești. In September 2011, he was suspended 10 games for breaking the leg of Băcilă, Pandurii Târgu Jiu"s player.
Southampton
On 14 August 2014, he joined Premier League side Southampton for an undisclosed fee, believed to be around €7.5 million, signing a four-year deal.
He made his first appearance as a substitute in a 3–1 victory at West Ham. His first start came on 23 September in a 2–1 League Cup victory over Arsenal.
He made his debut for the senior team in a friendly game on 8 February 2011, against Ukraine.