Sam Allardyce says he is “enthused and energised” about returning to management with Everton.
The 63-year-old former England boss has signed a deal until June 2019 to become the permanent successor to Ronald Koeman, who was sacked in October with the club 18th in the Premier League.
Allardyce has been out of work since leaving Crystal Palace in May.
“The ambition of the club, allied to all the fantastic history, has proved to be key for me,” he said.
“Obviously, the club has gone through a difficult spell and hopefully I can put that behind us as quickly as possible and start looking upwards again.
“I think that whatever’s happened before we’ve just got to all rally around together. Our will to do it all together would be my way forward.
“I feel really enthused and energised to come in as manager.”
Dutchman Koeman guided Everton to seventh place last season – his first in charge – but was sacked the day after a 5-2 home defeat by Arsenal on 22 October.
The Toffees spent more than £130m on new players in the summer but have struggled without last season’s top scorer Romelu Lukaku, who was sold to Manchester United for £75m in July.
Under-23 coach David Unsworth, a former Everton defender, was placed in temporary charge of the first team, and won two of his eight matches.
His final game before returning to his former role was Wednesday’s 4-0 Premier League victory over West Ham at Goodison Park, which Allardyce watched from the stands.
“Sam understands the long-term ambitions we have for this great club and I know he is a man who gives it his all and is focused 24 hours a day,” added Everton’s majority shareholder Farhad Moshiri.
“I would like to put on record our thanks as a club to David Unsworth for stepping up when we needed him over the last few weeks. He is a real Evertonian, embodying the commitment, pride and passion we all feel for the club.”
Everton are now 13th in the league and face Huddersfield on Saturday.
Allardyce left Palace after just five months – his first job since an ill-fated one-game spell as England manager – having led the club to eight wins in 21 games to secure a 14th-place finish in the league.