The 28-year-old Argentine is Aston Villa’s third summer signing, with manager Dean Smith having already secured the club record signing of Ollie Watkins from Brentford and Matty Cash from Nottingham Forest.
Martinez joined Arsenal from Indepediente in 2010 but played second fiddle for much of his time in North London and spent time on loan at Oxford United, Sheffield Wednesday, Rotherham, Wolverhampton Wanderers, Getafe and Reading.
Martinez impressed when he got a decent run of games under his belt towards the end of the 2019/2020 season after first choice Bernd Leno got injured.
Martinez made nine Premier League appearances last season and was in goal when Arsenal beat Chelsea and Liverpool in the FA Cup final and Community Shield respectively.
He decided to move on after Mikel Arteta restored Leno as Arsenal’s first choice between the sticks this season.
"We are really pleased with the signing of our new goalkeeper Emiliano Martinez," said Villa head coach Dean Smith.
"We know how highly Arsenal rated him and we watched his outstanding performances last season in a trophy-winning top side.
"We moved for Emi when we saw the opportunity, as it is rare to be able to buy a top-class goalkeeper who hasn't yet reached their peak age and who can therefore be a key player for our club for the long term."
Martinez could make his Aston Villa debut in their Premier League opener against Sheffield United on Monday.
