It is understood a deal has now been agreed between the two clubs, believed to be worth around £30 million, for the 25 year-old, who could be unveiled on Thursday once all the formalities are complete.
The Gunners are also expected to bring in France defender Mathieu Debuchy from Newcastle as manager Arsene Wenger looks to build on last season’s FA Cup final success.
Bringing in Sanchez, who also had interest from Liverpool and Juventus, will present something of a personal coup for Wenger, who is understood to have spoken to the player face-to-face while working for French television at the World Cup in Brazil, convincing him Arsenal was the right place to further his career.
The Gunners, though, continue to work on bringing in other reinforcements to mount a long-overdue sustained assault on the Barclays Premier League title, having been clear at the top in January only to fade away and finish fourth.
While Debuchy will represent a Premier-League ready replacement for Bacary Sagna, who left on a free transfer to Manchester City, Wenger also has his mind on further additions.
Queens Park Rangers forward Loic Remy, rated at around £8 million, is a potential target, having spent last season on loan at Newcastle, along with Bayer Leverkusen midfielder Lars Bender.
Reports have also linked Arsenal with Real Madrid’s German midfielder Sami Khedira, although any possible move could well hinge on the personal terms.
Arsenal also need a goalkeeper, with number two Lukasz Fabianski having joined Swansea.
Midfielder Mikel Arteta has no intention of leaving the Gunners, according to his agent, with reports linking the Spaniard with Fiorentina.
Wenger will return to Arsenal after the World Cup final, ahead of a trip to New York at the end of the month.
Arsenal host the Emirates Cup on August 2/3, before tackling Premier League champions Manchester City at Wembley in the Community Shield.