McLeish makes the move across the city just five days after resigning from his post at St Andrew's.
Villa have held off fierce opposition from their own supporters and a bitter row with Blues to bring in the 52-year-old.
Villa fans were celebrating on the final day of the season when McLeish took Brum down - having had a shocking campaign themselves.
McLeish was a laughing stock ... but now he takes over the Villa hotseat.
Blues, however, remain far from happy with the situation and are continuing to take legal advice.
The St Andrew's club accused their rivals of tapping up the former Scotlandboss earlier this week and demanded £5.4million in compensation to cover the remaining two years of his broken contract.
They also threatened to report Villa to the Premier League and take out an injunction to block the move and, although neither was carried out, they insist the matter is not yet over.
Villa chief executive Paul Faulkner said: "We believe we have appointed the right man for the job.
"Unquestionably, Alex meets the criteria we set out at the beginning of our search which was based on proven Premier League experience, leadership, a hard-working ethic and, most importantly, a shared vision for Aston Villa."