Kiviniemi won the post in a second round of voting at the Centre Party congress in Lahti 1357-1035 in which she was matched against Employment and Economy Minister Mauri Pekkarinen.
She is likely to take over the Prime Minister's portfolio from Matti Vanhanen in about a week's time.
The 41 year-old Kiviniemi holds a Master's degree in political science and has been an MP for 15 years. Her career includes a year as Prime Minister Vanhanen's economic policy advisor and a six-month stint as Minister for Foreign Trade and Development. She is Minister of Public Administration and Local Government in the present coalition.
Kiviniemi is from Jalasjärvi in South Ostrobothnia and currently is a resident of Helsinki. She is married and has two children. Her husband works in advertising. She has said that she has a special interest in children and young people, as well as music.
Following her win on Saturday, Kiviniemi said that she is more than ready, more than motivated and more than excited about her new duties.
She thanked her predecessor, Matti Vanhanen, for his cooperation and expressed hope that it will continue.
Kiviniemi's appointment as Prime Minister will still require parliamentary and presidential approval. If she takes up the post, she will be Finland's second woman Prime Minister. The first, Anneli Jäätteenmäki, also of the Centre Party, was in office for barely two months in 2003 before being replaced by Matti Vanhanen amid a political scandal.
Also on Saturday, the Centre Party congress elected Timo Laaninen as party secretary. He defeated the incumbent, Jarmo Korhonen, 1675-579. Laaninen is the editor-in-chief of the Centre newspaper Suomenmaa and a former special political assistant to Prime Minister Vanhanen.