The pair were confirmed by European Ryder Cup captain Jose Maria Olazabal at a press conference in Glenaeagles.
It means 29-year-old Colsaerts, the only uncapped player in Europe's side, will become the first Belgian to play in the competition.
Poulter's inclusion means no place, as expected, for Padraig Harrington, who has featured in the last six Ryder Cup teams for Europe.
While Harrington has won only two of his last 13 cup games Poulter has won seven of his last eight and Olazabal has rewarded the two players who came closest to making the team on points.
Poulter finished 11th on the table and Colsaerts 12th. Harrington was down in 19th place.
US captain Davis Love will name his four wild-card picks for the USA team next week. This year's competition takes place at Medinah, Chicago, from September 28-30.
The European 2012 Ryder Cup team:
Rory McIlroy, Justin Rose, Graeme McDowell, Paul Lawrie, Francesco Molinari, Luke Donald, Lee Westwood, Sergio Garcia, Peter Hanson, Martin Kaymer, Ian Poulter, Nicolas Colsaerts
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