It faced stiff competition from rival Grassroots Out, which had the backing of Leave.EU, whose application was also deemed to be "of a high standard" by the elections watchdog, while an application from the Trade Unionist and Socialist Coalition "did not demonstrate that it adequately represented other campaigners", the commission said.
On the 'remain' side, the Britain Stronger in Europe campaign was the only applicant, and was duly awarded the designation.
The regulated campaign period begins on 15 April. Between this date and the 23 June vote, the two designated campaigns may spend a maximum of £7m - while other registered campaign groups are restricted to £700,000 - and other benefits. There are also restrictions on spending by political parties and by private business and other groups.
Information about how the decision was made has been posted on the Electoral Commission website.
Vote Leave is London-based, with Conservative peer Lord Lawson as its chair, and support from a cross-party group of MPs including Douglas Carswell, UKIP's sole MP. Leave.EU has repeatedly attacked it in public and attempted to paint it as a campaign based among the Westminster elite and the "establishment", and lacking popular support. Grassroots Out launched its campaign in Northamptonshire and has UKIP leader Nigel Farage and Tory Peter Bone among supporters.
Within half an hour of the announcement at 3pm on Thursday, Leave.EU had reportedly said it would challenge the decision through a judicial review.
The Telegraph reported that Leave.EU said that this could delay the referendum until October.
Leave.EU had also been upset yesterday when a since deleted Twitter post from a Conservative figure made it appear that the decision had been leaked ahead of the official announcement, something the Electoral Commission denied.
Outrage as Establishment 'Leave' Campaigner Claim Designation 36 Hours Before Announcement https://t.co/NIYAHMb6fO— Raheem Kassam (@RaheemKassam) April 13, 2016
Really? I do think the electoral commission need to dispel the idea that people have been tipped off . All very SW1 https://t.co/7vJhLCzNY8— Arron Banks (@Arron_banks) April 13, 2016
Claire Bassett, chief executive of the Electoral Commission, said: "Where there are competing applicants for a particular outcome the law is clear; we must designate the applicant that appears to us to represent those campaigning for that outcome to the greatest extent."
Bassett said that both ‘leave’ campaigns were "high quality" but said it considered Vote Leave "better demonstrated that it has the structures in place to ensure the views of other campaigners are represented in the delivery of its campaign".
Speaking to PRWeek in the new edition of the magazine, out this week, Vote Leave comms director Paul Stephenson said that while the group had already been meeting and speaking regularly with Leave.EU and Grassroots Out, they would "work together a little more closely" following the designation.
Farage said: "Regardless of whichever campaign got the designation, UKIP would always have played a big role in this campaign as the only national party committed to leaving the EU and with a substantial £4 million spending limit. I have always wanted all on the Leave side to come together and have done my best to try and make this happen."