Niinistö, former chair of the conservative National Coalition Party, did not say what he plans to do after leaving Parliament. Niinistö has served as the Minister of Finance, Deputy Prime Minister and as a vice president of the European Investment Bank. In the 2007 elections he was elected to Parliament with a record number of more than 60,000 personal votes.
The newspaper reports that Niinistö informed Party Chair Jyrki Katainen of his decision in February.
Niinistö has been seen as a leading presidential contender. In the last election he lost to Tarja Halonen in the second round.