Knudsen, inspired by German theories, argued that "socialism [is] the only means" to "help the working estate".
He became a co-founder of the Norwegian Labour Party in August 1887 in Arendal.
Like the trade unions, the early Labour Party contained both socialist and non-socialist elements.
The most important political demand was universal suffrage.
Knudsen was a member of the central committee from the beginning, and then became party leader from 1889 to 1890 and 1900 to 1903.
From 1899 to 1926 he was a member of Kristiania city council.
He was elected to the Norwegian Parliament in 1906, representing the constituency of Grünerløkken, and was re-elected in 1909 and 1912.
For the first two terms he was the leader of the parliamentary party group.

Knudsen was a deputy member of the Norwegian Nobel Committee from 1913, and served his third term as party leader from 1911 to 1918.
His leadership came to an end when the radical wing, spearheaded by Kyrre Grepp and Martin Tranmæl, took over at the 1918 national party convention.
He left the central committee, but returned in 1920.
When the less radical wing broke out to form the Social Democratic Labour Party in 1921, Knudsen did not follow; he continued in the central committee until 1924.
In 1923 the name of the newspaper Social-Demokraten had been changed again, to Arbeiderbladet ('The Labour Paper').
It became the main organ of the Labour Party, undergoing direct control; the editor-in-chief was also represented in the national party board.
As the newspapers became independent in the latter quarter of the twentieth century, the newspaper changed its name again, to the current Dagsavisen.

Knudsen died in 1929.
Knudsen, inspired by German theories, argued that "socialism [is] the only means" to "help the working estate". He became a co-founder of the Norwegian Labour Party in August 1887 in Arendal. Like the trade unions, the early Labour Party contained both socialist and non-socialist elements. The most important political demand was universal suffrage. Knudsen was a member of the central committee from the beginning, and then became party leader from 1889 to 1890 and 1900 to 1903. From 1899 to 1926 he was a member of Kristiania city council. He was elected to the Norwegian Parliament in 1906, representing the constituency of Grünerløkken, and was re-elected in 1909 and 1912. For the first two terms he was the leader of the parliamentary party group.
Knudsen was a deputy member of the Norwegian Nobel Committee from 1913, and served his third term as party leader from 1911 to 1918. His leadership came to an end when the radical wing, spearheaded by Kyrre Grepp and Martin Tranmæl, took over at the 1918 national party convention. He left the central committee, but returned in 1920. When the less radical wing broke out to form the Social Democratic Labour Party in 1921, Knudsen did not follow; he continued in the central committee until 1924. In 1923 the name of the newspaper Social-Demokraten had been changed again, to Arbeiderbladet ('The Labour Paper'). It became the main organ of the Labour Party, undergoing direct control; the editor-in-chief was also represented in the national party board. As the newspapers became independent in the latter quarter of the twentieth century, the newspaper changed its name again, to the current Dagsavisen.
Knudsen died in 1929.
Christian Holtermann Knudsen