Everton have confirmed the appointment of Sam Allardyce as their new manager on an 18-month contract believed to be worth around £9m ($12.1m), bringing to an end a five-week search for Ronald Koeman's successor.

Former West Ham United and Crystal Palace boss Allardyce had ruled himself out of the running to take up the reins at Goodison Park around a fortnight ago after growing frustrated by the Toffees' approach to negotiations, but Farhad Moshiri and co restarted talks after the damning loss to Southampton and quickly thrashed out an agreement with the 63-year-old, who is set to take charge of his seventh Premier League club.

Allardyce was in the stands at Goodison on Wednesday night (29 November) alongside Moshiri and Everton chairman Bill Kenwright, watching over his new side's 4-0 victory over one of his old clubs West Ham. He will be positioned in the dugout on Saturday as the Merseysiders host Huddersfield Town, with interim boss David Unsworth re-assuming his position as manager of the club's Under-23 squad and Academy Director of Coaching.

Allardyce's backroom staff will consist of Sammy Lee, a divisive inclusion given his ties with Liverpool, former Leicester City boss Craig Shakespeare, Duncan Ferguson, Martyn Margetson and Rylands Morgan.

Many will be wondering just how Everton got to the stage where they felt it necessary to appoint Allardyce, but the former England boss has no interest in what they naysayers think about his arrival on Merseyside, which has given him a new lease of life just six months after retiring from football.

"The attraction of the club itself, the people I've known at the club – Peter Reid is one of my best mates, so are Andy Gray and Paul Bracewell whom I worked with at Sunderland – these people have always made me aware of just how special and unique a club Everton is and I feel really enthused and energised to come in as manager," Allardyce told the club's official website.

"I've always thought Everton was a great club. It is a great club. 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. Because, ultimately, it's the ambition of the club, the ambition of the owner and the board, allied to the fact that it's Everton and all the fantastic history, which have proved to be key for me.

"Ambition is important for any manager or coach, owner or director. It's what you need to have and hopefully we can deliver to the fans to get this club high up the league. That's what we're aiming for.

"I think that whatever's happened before we've just got to all rally around together. Because we are all in it together and let's all pull in the same direction. Let's try to get a healthy spirit around the club. That's difficult when you're losing but the win last night over West Ham and the magnificent atmosphere around Goodison, which was just brilliant, well that's lifted everybody around the club.

"The fans are the most important people at any football club, of course, and we have to give the players every possibility to play to their best, really give them no excuses for not playing to their best and get them right back up to the top level we believe they're capable of."

Allardyce was a free agent but Everton still managed to take five-and-a-half weeks to appoint him as their new manager. Approaches for Watford boss Marco Silva and Shakhtar Donetsk manager Paulo Fonseca were swiftly rebuffed by their respective clubs, but Moshiri, who has in come in for major criticism in recent weeks, has told of his happiness to see Allardyce arrive and also gave thanks to Unsworth, who was hung out to dry by Everton's officials.

"I'm delighted to confirm Sam as our new manager. His strong leadership will bring great motivation and get the best out of players," Moshiri said. "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 on the club.

"Evertonians are the most passionate and best fans in the world and when the Club does badly we all suffer. But in football everything changes very quickly, so I hope this will help to propel us to where we should be.

"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."

The arrival of Allardyce marks a significant shift in power at Everton, with long-time custodians Kenwright and Robert Elstone taking a backseat as Moshiri, director of football Steve Walsh and board members Keith Harris and Alexander Ryazantev searched for a new boss.

Ryazantev is primed to receive greater responsibility at Goodison Park in the coming months, according to the Times, while it remains to be seen if Kenwright and Elstone's influence diminishes further.

Jon Woods, Sam Allardyce and Farhad Moshiri
Allardyce and Moshiri watched over Everton's 4-0 victory over West Ham United on Wednesday Getty Images