The Pole, who drives for the LOTOS Rally Team, said the decision had been taken because of the number of technical problems that had affected his Mini so far this season.
Kosciuszko has pulled out of the upcoming Acropolis Rally and will make his Fiesta WRC debut on the Rally d'Italia in June.
Kosciuszko, 28, has also parted company from Motorsport Italia, the squad that ran the Mini. His Fiesta will be run by Ford’s former WRC partner, M-Sport.
Kosciuszko said: "I am a player who is committed to high standards and consistently strives to achieve the intended objective. The place where I got, the WRC, confirms my determination. The beginning of the season for us was technically very difficult, so I thank my strategic partner - Grupa LOTOS, which showed great understanding.
“Together we decided to change the car and work with M-Sport. I would like to thank Motorsport Italia for co-operation and wish them luck for the future."
M-Sport boss Malcolm Wilson said he was very happy to welcome Michal into his team: “He showed some impressive pace at the wheel of the Ford Fiesta S2000 in 2010 – securing a podium finish as part of the S-WRC in Mexico – and, considering his clear progression at WRC level, we’ll be hoping that he can challenge for some good results both this year and in the future.”
"The beginning of the season for us was technically very difficult,"