The 26-year-old Netherlands international is the third arrival at Goodison Park this month after Nathan Patterson and Vitaliy Mykolenko.
Everton and Villa have already done business this week, with Lucas Digne signing for Steven Gerrard's side after falling out with Rafael Benitez.
El Ghazi joined Villa initially on loan from Lille in the summer of 2018 and helped the West Midlands side gain promotion to the Premier League. He scored 10 goals in 28 top flight appearances last season but has been used sparingly since Gerrard replaced Dean Smith.
Speaking to evertontv, El Ghazi said: "I'm really excited. Everton is a big club, I cannot wait to get started.
"I've met a few fans already and it's great to see how people live for the club. It's basically their religion. You just want to give it your all and show them what you can do to make them happy.
"I just want to focus on working hard, getting into the team, fighting for my place and, with the boys, to get Everton where it belongs - that is much higher up the table. We have a really good squad.
"I've played at Goodison Park a few times now and it's a beautiful stadium.
"It's a bit different than other stadiums and that's what makes it quite unique. I'm really looking forward to playing there for Everton.
"We have a really strong squad. The wingers are doing well and have a lot of quality. It will be hard work but competition with others is good and that is how you achieve great things.
"I will work hard and give everything I have. That is the least you can expect from a player. That is what I will start with and from there hopefully, I will be able to score goals and give assists."
El Ghazi could make his debut against Norwich City this weekend.
