Until Uusipaavalniemi's defection Thursday, the Centre and the National Coalition both had 51 members in Parliament.
Uusipaavalniemi is a first-term MP from the Uusimaa electoral district. As a Centre Party member, he was a vocal critic of the government's economic policies.
He became a publicly-known figure as the captain of Finland's curling team that took the silver medal at the last Winter Olympics.
According to National Coalition Party chair, Finance Minister Jyrki Katainen, the new position of his party as the single largest bloc in Parliament will not affect government cooperation.