But the regulator also said it would "not be appropriate" to add the Green Party to its "major parties" list.
The Conservatives, Labour and Lib Dems remain on the list, alongside the SNP in Scotland, Plaid Cymru in Wales and five parties from Northern Ireland.
Party broadcasts on the BBC are regulated separately by the BBC Trust.
The tradition of allowing free airtime for party election broadcasts is seen as a substitute for paid political advertising on TV and radio, which is banned in the UK.
Ofcom's statement, which will apply to outlets including ITV, Channel 4 and Talksport, follows a consultation into which parties had the "significant levels of support" required to get at least two broadcasts.
Other parties who are standing in at least a sixth of all seats are entitled to at least one broadcast.
Green Party leader Natalie Bennett said she was "deeply disappointed" by the draft Ofcom ruling when it was published for consultation in January.
The regulator said it based its final decision, which is in line with the draft proposals, on consultation responses, "evidence of electoral performance" and polling trends.
The Green Party recently said it had more members than UKIP, but Ofcom said party membership was less "robust" as an indicator because it only relates to a small proportion of the total electorate.
UKIP chairman, Steve Crowther said the ruling was "simply a recognition of what everybody knows" given UKIP's recent electoral performances.
The UK Independence Party has been added to the list of parties entitled to at least two party election broadcasts, Ofcom has said.