The decision means Ukip will be given the same status as the Conservatives, Labour and Liberal Democrats for election broadcasts and news coverage of the May 22 contest.
But Ukip's limited support in Scotland means it will not have to be treated as a major party by broadcasters north of the Border or in news coverage focusing solely on Scottish constituencies.
Ukip director of communications Patrick O'Flynn said: "This Ofcom decision was a fairly obvious one given the success of Ukip over the past few years.
"It makes no sense for patterns of coverage to be based on patterns of electoral support that pertained four years ago. Ukip is a major player in British politics now."
The Ofcom ruling means that broadcasters transmitting party election broadcasts on a UK or Great Britain-wide basis, such as Channel 5 in the European parliamentary elections, will be obliged to treat Ukip as a major party, in the same way they would the Tories, Labour or Lib Dems.
STV will not be required to treat Ukip as a major party for the purposes of broadcasting Scotland-only party election broadcasts because Nigel Farage's party has "low levels of support" in the country, Ofcom said.
But ITV Wales will have to treat Ukip as a major party due to the "significant levels of support" there.