Sportsmail exclusively revealed Hammers co-owners David Gold and David Sullivan's move for Allardyce on Saturday morning.
Back in the game: Sam Allardyce will attempt to restore West Ham's Premier League status
And the former Newcastle manager's advisors spent Tuesday thrashing out terms over the 56-year-old's move to Upton Park, which includes a substantial bonus for promotion.
Allardyce, 56, said: 'I look forward to taking charge after I have had a family holiday. It's always difficult dealing with the aftermath of relegation but I want to get West Ham back into the PremierLeague as quickly as possible.'
Double act: West Ham's co-owners David Gold and David Sullivan have moved swiftly to replace Avram Grant
The Hammers hierarchy are completing the formalities to the deal which will see Allardyce replace Avram Grant.
Allardyce's appointment brings to an end the club's two week search for a new manager.
Martin O'Neill, Alex McLeish, Neil Warnock and Dave Jones were all serious contenders for the role.
Friends reunited: Neil McDonald will be named as Allardyce's No 2 at Upton Park
Allardyce has been out of work since his shock sacking by Blackburn last December.
The Hammers' new boss is expected to bring his former Ewood Park No 2 Neil McDonald with him to East London.
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Explore more:People: Martin O'Neill, Neil Warnock, David Gold, Alex McLeish, David Sullivan, Sam Allardyce Places: Newcastle, London