The Hornets have agreed a deal worth over £1.5million for the top prospect, who has been a regular in League Two
Wilmot was taken out of the Stevenage side at the weekend as the clubs finalised the terms.
And he should be clear to sign this week before joining officially in the window.
Stevenage are happy to have the cash and will also try to bring Wilmot back on loan further down the line.
Watford have seen off Premier League champions Chelsea in the chase and are offering a quicker route to the first team than their much richer rivals.
Stevenage chairman Phil Wallace revealed last month that Liverpool, Burnley, Brighton and Bournemouth have also monitored Wilmot’s progress.
The Hertfordshire club have known a deal was close for several days.
And when the starlet was left out against Newport on Saturday Wallace said: “Ben came back from international duty and we have had developments that suggest a deal will be agreed shortly for him to move when the window opens.
“We have had interest from Premier League and Championship clubs, which is not surprising when Ben is recognised by England as being one of the top four centre halves at his age level, with the other three coming from Man City, Chelsea and Spurs.