Saarinen was a stonemason who joined the local labor union branch in 1934. During World War II he fought for the Finnish troops. Saarinen was later known as one of the most prominent Communist leaders outside the Eastern Bloc. He was considered as a Eurocommunist who had sceptical views over the Soviet Union. Saarinen condemned the 1968 invasion of Czechoslovakia and during the 1970s, he resisted the efforts of the Stalinist extremists like Taisto Sinisalo to increase the Soviet influence in Finland.