The 29-year-old winger had been linked with the Birmingham club for several days and will spend the duration of the 2018-19 campaign at Villa Park.
DR Congo international Bolasie had become a peripheral figure at Everton under Marco Silva, and Steve Bruce’s men have taken advantage of the Championships’ prolonged loan window to sign a man who was an FA Cup finalist with Crystal Palace in 2015.
Speaking to Villa’s official website, he said: “My main aim here is to get this club promoted. A club of this stature has to be in the Premier League.
"I looked around both Villa Park and the training ground, and me and my family just said: 'Wow.' It's Premier League everywhere you look.
"I'm here to make myself smile again and use all my ability to try and help the team. It's great to be here."
Bolasie has previously turned out for Barnet, Plymouth and Bristol City, and has scored 11 Premier League goals in 119 outings at the top level.
Signed by the Toffees from Palace for £25 million (€27m/$32m), a serious knee injury that saw him ruled out for the best part of a year disrupted his time at the club, however.
Meanwhile, Everton are still waiting for further bids for England Under-21 international Ademola Lookman, whose move to RB Leipzig appears to have terminally broken down.