Together with the left-socialist opposition inside the social democrats, he left the party in 1917 and formed Sweden's Social Democratic Left Party, with the Social Democratic Left-Group as their parliament party. From the early Riksdag from 1919 to 1930 (communist) Winberg belonged to the upper house of the Riksdag (första kammaren or First Chamber) for the constituency of Norrbotten County until 1921 and from 1922 onwards, he served the constituency of Västerbotten and Norrbotten County.
Winberg served in the upper house of the Swedish Riksdag (First Chamber) from 1919 to 1930, representing Norrbotten County until 1921 and then Västerbotten and Norrbotten County after that. He left the Social Democrats in 1917 and formed Sweden's Social Democratic Left Party, which was represented by the Social Democratic Left-Group in parliament.