He played in the same Auxerre team as Abou Diaby, a future Arsenal teammate, and Watford centre-back Younès Kaboul.

[10] Sagna made his debut for Arsenal on 19 July 2007 as a starter in the squad that beat Turkish club Gençlerbirliği 3–0 in a friendly at Austria's Bad Waltersdorf Stadion.

Sagna stated, "I love Arsenal, it's a great club," and further added, "The manager is also very good and next season we will be fighting for all the trophies."

He provided many assists though, his most important contribution arguably being the cross to striker Nicklas Bendtner, who gave Arsenal the 1–0 lead in the 94th minute against Wolverhampton Wanderers.

[16] On 13 August 2011, Sagna started and played the full 90 minutes against Newcastle United at St James' Park in a 0–0 draw on the opening day of the 2011–12 Premier League season.

On Saturday 20 August, he started at left-back and played the full 90 minutes in a 2–0 defeat at the hands of a Liverpool side that picked up its first win over the Gunners away from home in 11 years.

Sagna sustained a leg break during a match against North London rivals Tottenham Hotspur after a challenge by Benoît Assou-Ekotto forced him to land awkwardly.

On 26 February 2012, he started in the North London derby against Spurs, scoring a header from a Mikel Arteta cross and inspiring Arsenal to come back from being 2–0 down to go on and win 5–2.

On 9 February 2013, due to an injury to centre-back Laurent Koscielny during warm-ups, Sagna was forced to fill in as a central defender against Sunderland.

[23] He scored his first goal of the season, his fifth in Arsenal colours, against Stoke City on 22 September, heading in Mesut Özil's free-kick, securing a 3–1 win for the Gunners.

[24] On 17 May, Sagna started in the 2014 FA Cup Final as Arsenal beat Hull City 3–2 at Wembley Stadium, his first trophy at the club.

Sagna received his first senior international cap for France on 22 August 2007 in a friendly match against Slovakia on the road, which they won 1–0, coming on as a substitute for François Clerc after one hour of play.

He went on to make his competitive debut for France in their 6–0 away win at the Faroe Islands on 13 October 2007 in the UEFA Euro 2008 qualifiers, playing all 90 minutes.

He was not a candidate to join the French team at the Euro 2008 finals in Austria and Switzerland as he was still recovering from the injury sustained in Arsenal's Premier League match at Chelsea in March 2008.

After recovering from the injury, Sagna returned to the French team for their friendly match against Sweden in August 2008, playing all 90 minutes in a 3–2 away win.

He was also a part of the disastrous French World Cup campaign when the team crashed out at the group stage after losing 2–1 against hosts South Africa.

[37] On 31 March 2011, Sagna became an ambassador for Grassroot Soccer, an international non-profit that uses the power of football to educate, inspire, and mobilise communities to stop the spread of HIV.