Martinez has been with the Gunners for a decade, but has only been kept as an understudy or even as the third-choice goalkeeper during his time at the club.
However, he got his opportunity to shine in the latter stages of the 2019/20 campaign after Bernd Leno got injured, which allowed him to start in goal in a series of matches in the Premier League as well as the FA Cup, which Arsenal would go on to win.
Leno has always been viewed as the club's number one goalkeeper, though, which would have led to Martinez dropping to the bench again.
His performances after lockdown gained many admirers, no one more so than Villa who have now signed him on a permanent deal.
Manager Dean Smith says the club couldn't pass up the opportunity to sign the Argentine when it presented itself.
"We are really pleased with the signing of our new goalkeeper Emiliano Martinez," the Villa boss told the official club website.
"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 therefore can be a key player for our Club in the long term"
Martinez is Villa's third major signing of the transfer window after they recruited Matty Cash from Nottingham Forest and Ollie Watkins from Brentford for combined fees in excess of £40m