Antti Ilmari Lindtman is a Finnish politician who has served as leader of the Social Democratic Party (SDP) since September 2023. He has been the chairman of the city council of Vantaa since 2009 and a member of the Parliament of Finland for Uusimaa since April 2011. In April 2015, he was elected as the chairman of the Social Democratic Parliamentary Group.

The Social Democratic Party of Finland is a social democratic and pro-European political party in Finland. It is the third largest party in the Parliament of Finland with 43 seats. Founded in 1899 as the Workers' Party of Finland, the SDP is Finland's oldest active political party and has a close relationship with the Central Organisation of Finnish Trade Unions. It is also a member of the Party of European Socialists, Progressive Alliance, Socialist International and SAMAK.