Campbell joined Arsenal in 2011 and was thereafter loaned out to French side Lorient, Spanish club Real Betis and Greek outfit Olympiacos.

[7] On 28 July 2011, Costa Rican television reported that Campbell had come to an agreement with Arsenal,[8] after having been discovered by club scout Danny Karbassiyoon.

[10] On 6 August, Costa Rican media reported that Campbell was set to sign a five-year deal with Arsenal, after rejecting moves to Sevilla and Fiorentina.

[12] On 19 August 2011, Arsenal confirmed that they had signed Campbell,[13] but it was reported eight days later that he had failed to obtain a work permit to enable him to play in England.

[20] Campbell played 28 league matches and scored two goals; his first was on 2 December, to give Betis a 3–2 away win against Deportivo de La Coruña,[21] and his second came in the seventh minute of a 2–0 home victory against Levante on 13 January.

[28] He made his Premier League debut on 23 August in a 2–2 draw against Everton at Goodison Park, coming off the bench to replace Alex Oxlade-Chamberlain on the 74th minute of the match.

[28] Campbell's first Arsenal start came in the third round of the League Cup on 23 September, lining up in attack with Alexis Sánchez and Lukas Podolski in a 1–2 home defeat against Southampton.

[32] After returning from his loan at Villarreal, Campbell started his first game of the season in a 2–1 win against Tottenham Hotspur in the League Cup third round on 23 September 2015.

[33] On 31 October, due to injuries to Theo Walcott and Alex Oxlade-Chamberlain,[34] Campbell made his first Premier League start for the club against Swansea City at the Liberty Stadium, scoring his first competitive goal in a 3–0 win.

[35] The sides faced at the Emirates again in the FA Cup third round on 9 January 2016, with Campbell again scoring Arsenal's first as they matched the scoreline they achieved just over a month earlier.

On 28 July, in the 2016 MLS All-Star Game in San Jose, California, Campbell won an early penalty when fouled by Laurent Ciman, and took it himself to open a 2–1 victory.

In their group opener on 5 June at Cowboys Stadium, he replaced Marco Ureña in the 56th minute and a quarter of an hour later volleyed a goal to conclude a 5–0 win over Cuba.

[50] In the quarter-finals at the MetLife Stadium, he again came on for Ureña in the second half of extra time; the game went to a penalty shootout in which Campbell netted his attempt but Honduras advanced 4–2.

In their second group game, on 7 July at the Estadio 23 de Agosto in Jujuy, he concluded a 2–0 win over Bolivia after being set up by Heiner Mora, and was also fouled for Wálter Flores' red card.

[52] In September 2013, Campbell became the subject of controversy when video emerged of his off-the-ball dive against the United States' Matt Besler in a World Cup qualifying match.

[57] On 14 June 2014, Campbell scored Costa Rica's first goal in the 2014 FIFA World Cup, equalising against Uruguay in an eventual 3–1 victory.

[58] During the round of 16, Campbell was the fourth of five Costa Rican players to successfully convert his kick in a 5–3 penalty shootout victory over Greece.