The move is intended to lead to more comprehensive case histories being submitted for integrated campaigns to which a variety of communications specialists may have contributed.
It means the 2004 competition will be open to direct marketing, PR, sales promotion and sponsorship agencies.
Tim Broadbent, the chairman of the IPA's value of advertising committee, said: "In 2002, we relaunched on a media-neutral platform with great results and we see opening up the competition as a logical step in consolidating the Effectiveness Awards."
To enter the awards, non-IPA member shops will have to abide by a number of conditions. These include paying a special non-member rate and attending at least one of the IPA's "How to win" seminars.
Sir Niall Fitzgerald, the Unilever chief executive, will head the judges for the awards, for which the closing date will be 21 May 2004.