Berardi started his career at Swiss club Lugano's youth team. In the summer of 2005, he was signed by Serie B side Brescia. Berardi made his professional debut on 30 June 2007, in a winning away game against Pescara (1–3).
In his first season, Berardi made ten appearances in all competitions under the management of Serse Cosmi. In the 2008–09 season, Berardi was used in 26 Serie B games. Before finally becoming a first team regular in Giuseppe Iachini team during the 2009–10 season, Brescia earned promotion to Serie A after beating Torino in the Serie B play-offs.
Berardi made his Serie A debut on 12 September 2010 in a 3–2 victory against Palermo. He made 26 starts in total for Brescia in Serie A, although Brescia were relegated at the end of the season after finishing in 19th position.
On 12 January 2012, Berardi linked up with his former Brescia manager Giuseppe Iachini who signed him for Sampdoria. Berardi made his debut in a 2–1 victory against Padova on 14 January. At the end of the 2011–12 season, Berardi gained his second promotion to Serie A after winning the Serie B play-offs by beating Varese 4–2 on aggregate in the two-legged play-off final.
The following club season in Serie A, despite stiff competition from Italian international Lorenzo De Silvestri, Berardi made 21 appearances in Serie A during the 2012–13 season. However, after the club appointed Siniša Mihajlović as head coach in November 2013, Berardi lost his place in the starting lineup and only made five Serie A appearances during the subsequent 2013–14 season.
On 19 July 2014, Leeds United announced that they had signed Berardi to a two-year deal for an undisclosed fee, with an option of a third year. Club president Massimo Cellino confirmed that Berardi had taken a wage cut to join Leeds. On 1 August, Berardi was assigned the number 12 shirt for the 2014–15 season.
Berardi made his Leeds debut on 12 August 2014, starting the League Cup match against Accrington Stanley. He was sent off on his debut for a straight red card. As a result of his red card, Berardi picked up a three-match ban, missing matches against Middlesbrough, Brighton & Hove Albion and Watford. With regular right back Sam Byram suspended, Berardi was set to start against Bradford City on 27 August, but was ruled out after picking up a concussion the day before the game. His full league debut was in a 1–1 draw away at Birmingham City on 13 September 2014.
On 20 September, Berardi received his second red card in just his fourth game, after being sent off in a 3–0 win over local rivals Huddersfield Town.
With regular left back Charlie Taylor pushed forward into an attacking left wing position, during 2015 Berardi became a regular fixture in the left-back position for Leeds. Berardi finished the season in strong form at left back, starting 10 of the last 11 games and becoming a fans' favourite for his performances.
Berardi was given the number 28 shirt for the 2015–16 season. On 21 September 2015, after becoming a highly popular player with the fans for his consistent displays at both right back or left back positions, Berardi signed a two-year contract extension with the club lasting until 2018.
On 21 November, Berardi received another straight red card for Leeds in a match against Rotherham United after being left with a bloodied nose by an elbow to the face from Leon Best (which he also received a straight red for); Berardi reacted angrily by pushing Best to the ground before being restrained by teammates. The ban was later reduced after appeal due to the severity of the elbow Berardi received from Best, provoking the reaction.
After returning from suspension, on 14 December Berardi suffered a torn ankle ligament against Charlton Athletic which ruled him out for two months. After returning from injury, in April 2016, in the return fixture against Rotherham, Berardi – in similar circumstances to the reverse fixture – suffered a bloodied face/head injury after being elbowed by Rotherham striker Matt Derbyshire, which resulted Derbyshire being given a straight red, albeit in a 2–1 defeat for Leeds.
On 19 April, Berardi was nominated for the Leeds United Player of the Year award, alongside Charlie Taylor, Liam Bridcutt, Mirco Antenucci and Lewis Cook. Berardi also finished second in the voting for the Yorkshire Evening Post Player of the Year award after coming second to eventual winner Taylor. The official Leeds Player of the Season award was won by Taylor on 30 April.
Berardi missed the entirety of Leeds' 2016–17 pre-season friendlies due to injury, although he did return to the substitutes' bench for the final pre-season friendly against Italian side Atalanta. On 7 August, in the opening fixture of the season against QPR in a 3–0 defeat, Berardi was substituted early in the first half after picking up a hamstring injury. As a result of the hamstring injury, Berardi was ruled out for around 6 weeks.
On 26 October 2016, Berardi made his long awaited return from injury for Leeds when he started in Leeds' penalty shootout victory against Norwich City in the English League Cup, after a dramatic 2-2 draw in normal time. However upon his return from injury, Berardi was kept out the side due to the impressive form of new right back Luke Ayling. After an Achilles injury to regular left back Charlie Taylor, on 29 December 2016 against Aston Villa, Berardi came into the side as Left Back for a run of games. Berardi's form at left back managed to keep out the returning Charlie Taylor for the remainder of the season.
On 6 August 2017, Berardi suffered a dislocated shoulder in the 3-2 victory against Bolton Wanderers in the first game of the season, and had to be replaced by debutant Vurnon Anita in the 1st half. On 8 August, Berardi signed a new 3 year contract at the club, keeping him at Leeds until the end of the 2019/20 season.
After playing for the Switzerland national under-20 team, Berardi debuted for the Switzerland U21s against Greece on 19 November 2008.
Berardi played his first match for Switzerland at senior level against Liechtenstein on 10 August 2011.As of 19 September 2017.
Play-off winner 2009–10
Play-off winner 2011–12