Charles Macnamara (Charlie) O'Brien (March 2, 1875 – February 23, 1952) was a Canadian socialist activist and politician in Alberta, Canada.

[2][4] O'Brien was a skilled orator and author,[3] drawing comparisons to prominent activists such as Bill Haywood, Jack London and Eugene V.

He was elected to the Legislative Assembly as a member of the Socialist Party of Alberta, narrowly defeating Liberal John Angus Macdonald by 32 votes.

[3] The first Socialist elected to the legislature, the vote "reflected a growing radicalization" among Alberta coal miners, O'Brien's core constituency.

The Socialists deserve great credit for the way every man of them got out and hustled; also the supporters of the Independent who were made up of, principally, the working classes—including Dagos and Slavs who neither read, write, or speak, our language.

[10] He also participated in the Alberta and Great Waterways Railway debate and set a provincial legislative record for filibustering with a speech to the house on February 13, 1912, that lasted five hours and fifty minutes; he still had not finished when the session was adjourned late at night.