The Hornets have reportedly agreed a deal with the League Two side worth over £1.5m to bring the highly-rated 18-year-old to Vicarage Road.
It was reported last weekend that Wilmot was withdrawn from the Stevenage squad on Saturday due to transfer negotiations, and it appears that Watford won the fight to land the England Under-19 star.
Tottenham and Arsenal were reportedly in pursuit of the youngster, and both are thought to have had offers rejected in the past. A host of other Premier League sides were also supposedly interested in the defender, including Liverpool, Chelsea and Bournemouth.
Following Wilmot's withdrawal from the squad on Saturday, Stevenage chairman Phil Wallace revealed to the Sun: "
"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."
Wilmot was the only player outside of the top two English leagues to be representing the under-19s in their European Championship qualifiers.
The young defender is expected to sign for the Hornets this week after seemingly choosing Javi Gracia's side over many of the top six clubs, with first team football much more likely at Vicarage Road.