The club confirmed the news via its Twitter account:
Manager Arsene Wenger commented on Sanchez's arrival in a statement on the club website:
Alexis will add power, creativity and much quality to our squad and we are all looking forward to him joining up with us in a few weeks. He has consistently produced top-quality performances at the highest level for a number of seasons now and we are all excited to see him integrate into the Arsenal squad.
Sanchez also issued a statement on his move to England:
I'm so happy to be joining Arsenal, a club which has a great manager, a fantastic squad of players, huge support around the world and a great stadium in London. I'm looking forward to meeting my new team-mates and to be playing for Arsenal in the Premier League and Champions League.
Following his impressive La Liga and World Cup campaigns, the 25-year-old became one of the most in-demand attackers in the world.
At first, it seemed Suarez's transfer to Barca would hinge on Sanchez heading to Liverpool. Chris Bascombe of The Telegraph reported that the Reds would accept the Chilean and a lesser fee in lieu of the £70-80 million they were asking for the Uruguayan forward.
The Guardian's Andy Hunter also reported Liverpool would officially signal their interest in signing Sanchez:
However, the Daily Mail's David Kent reported Sanchez personally preferred a move to Arsenal:
Sanchez looks likely to snub a move to Anfield, with his heart set on a switch to the Emirates Stadium.
That means only a straight cash deal for Suarez is likely to be enough to persuade Liverpool to sees [sic] their prolific striker.
Sources close to Sanchez have indicated that the 25-year-old would prefer a move to London, leaving Arsenal in pole position to land the talented forward.
Once Barcelona tabled a £70 million cash bid for Suarez, per Hunter, that seemed to signify the Reds wouldn't in fact be getting the playmaker in return.
Spanish football journalist Guillem Balague reported Sanchez had some other options:
Liverpool's loss is Arsenal's gain.
Sanchez showed promise in his teenage years in South America and parlayed that into a move to Udinese in 2008 at 19. At the Stadio Friuli, he established himself as one of the most promising players in Europe.
Financial realities meant the Bianconeri were forced to sell off Sanchez, as they had to do with Gokhan Inler, Samir Handanovic, Juan Cuadrado, Mauricio Isla and Kwadwo Asamoah.
Upon arriving at the Camp Nou, Sanchez failed to recreate his form at Udinese. He dealt with both injuries and an inability to crack the first team on a regular basis.
Across the 2011-12 and 2012-13 La Liga seasons, he made a combined 38 starts and 16 substitute appearances, scoring 20 goals and recording 14 assists.
Sanchez had flashes of brilliance during those two tough seasons. After Barcelona's 2-1 Copa del Rey first-leg quarter-final win over Real Madrid in 2012, then-manager Pep Guardiola said, per Goal's Mark Doyle:
I want to especially thank Alexis [Sanchez]. He has played a fantastic game. He has stolen my heart.
He is very young, but he came forward and sacrificed himself a lot. He is a very humble person. I think the club has made a special signing. When he is fully settled, he will do even better.
This past season, Sanchez turned those flashes of brilliance into sustained, consistent production. He enjoyed his best year at Barca, scoring 19 goals in 34 La Liga appearances. His wondergoal against Real Madrid back in October was among the best all season across Europe's top leagues.
According to WhoScored.com, he was the second-highest-rated player for Barcelona (7.52).
Sanchez carried this strong form into the World Cup, helping Chile reach the round of 16 before losing to Brazil on penalties. He was one of the tournament's most dynamic players and spearheaded what was one of the most enjoyable teams to watch.
Arsenal couldn't be getting Sanchez at a better time in his career. He'll be riding a wave of confidence from the World Cup and will likely carry a chip on his shoulder after being sold by Barcelona.
Tactically, the Chilean star can be deployed anywhere across the attacking line; however, he spent the majority of his time with Barcelona on the right wing. Although he's a right-footer, Sanchez does most of his damage cutting in from the right and taking shots on goal rather than crossing into the box for his striker.
There will likely be a slight transition moving to the Premier League, but it shouldn't be as big of a problem as it was for him in Spain.
Few transfers made this summer will have a greater impact than Sanchez's move to the Gunners.
Note: All stats are according to ESPN FC unless otherwise noted.