The Hornets have signed a deal with temporary structures specialist GL Events.
The new East Stand will provide 3,000 extra seats formed from “steel frame supports and concrete row bases” alongside new modular changing facilities.
Watford CEO Scott Duxbury said: “We said at last season’s Fans Forum that once attendances were regularly reaching and exceeding 15,000 there would be a clear mandate to build the East Stand – and we’re delighted to be delivering on that now.
“Working with the expertise of GL Events, I am certain the East Stand will be a construction of which we can all be very proud – and will finally complete the stadium.”
Vicarage Road has enjoyed three 16,000-plus attendances at its first three home league matches of this campaign.