The Hornets revealed 10 days ago that they had agreed a deal in principle to sell to the Italians, who already own Serie A side Udinese and Spanish club Granada.
And the formalities of the agreement have now been signed, passing ownership from Laurence Bassini, who bought the npower Championship club 15 months ago.
Andrew Andronikou, partner at accountancy group UHY Hacker Young, which advised Watford on the sale, said: "We are delighted to have ensured that Watford F.C.'s immediate future is safe, and the fans can now focus on what we hope will be a successful 2012-13 season on the pitch.
"The Pozzo family has a proven track record of both building successful teams on the field, and balancing the books off the field. This transaction is a significant one as it provides the Pozzo football dynasty with a secure platform to introduce its successful formula to the UK.
"We feel that today's sale is an excellent outcome for both sides and it provides the club with stability moving forward. We wish Watford every success and look forward to seeing the team build on the improvement we saw last season."
Watford were forced to release an official club statement last Friday stressing the takeover remained on track after Bassini, in a newspaper interview, insisted the deal was off, stating the interested party "don't have the money".
And, with the deal now complete, the Italian family will look to put their own stamp on matters at Vicarage Road.
Gianfranco Zola has been heavily linked with a prospective role and only time will tell whether he is installed as the club's new manager.
Current boss Sean Dyche enjoyed a successful debut campaign in charge last season, guiding Watford to an 11th-placed finish - their highest league position for four years.
Source: PA
Source: PA