The new church body will represent more than 80 million Reformed Christians around the world and has been tentatively named the World Reformed Communion, although alternative names are being explored by WARC's Executive Committee.
A vote was taken to combine WARC and the REC on Monday following two days of detailed discussions on what shape a new joint Reformed body might take.
"This is a truly, truly important moment," said WARC president Clifton Kirkpatrick after the vote was taken at midday. He invited the participants in the meeting to join together in the singing of the doxology.
"It's a great moment," added REC president Douwe Visser. "I hope we can combine the efforts of these two organizations and have an even broader outreach than WARC and REC have at the moment."
"I have a feeling this new body will be the voice of the Reformed world."
WARC general secretary Setri Nyomi said, "This is a historic moment. The Reformed family has demonstrated that we have the ability to engage together in a united fellowship and overcome divisions - and for this we are thankful to God."
The decision follows a meeting in March at which the REC's Executive Committee approved the formation of a new Reformed body under the provisional name of the World Reformed Communion.
On Monday, the WARC leadership, however, has asked for more time to consider an alternative name for the body.
Richard van Houten, REC's general secretary, welcomed the move. "I'm delighted," he said. "I get the feeling the WARC Executive Committee really wrestled hard with some serious issues and in doing so, are now solidly behind the effort."
The new Reformed body will act as an umbrella organisation for WARC and REC's members, as well as those belonging to other Reformed, Presbyterian, Congregational, Waldensian, First Reformation, United and Uniting traditions.
WARC and REC said one of the key callings of the new body was to "foster Reformed confessional identity and communion among Reformed churches, and unity in the whole church".
The possibility of a uniting General Council has also been put forward for 2010 to solidify WARC's and REC union.
At the start of WARC's 10-day Executive Committee meeting in Trinidad and Tobago, Kirkpatrick urged WARC members to claim back unity in Christ.
"While the call to communion is a core Reformed conviction, it is often not a Reformed virtue these days. When we disagree with one another, all too often we end up splitting," he stressed.
"We are being called to claim the unity given in Christ... Support one another, be a community and a communion. We are called to go together for the long haul for the sake of the peace and reconciliation of the world."