He worked as a journalist and editor, going on to be hired as an editorial secretary by Hjalmar Branting at The Social Democrat.

[4] Bergegren supported direct action and in a speech at the second SAP Congress in 1891, he argued that social democrats should be prepared for "any violence whatsoever" and that this involved teaching "workers how to manufacture and use dynamite and daggers.

[9] As the party leadership moved to the right, Bergegren was expelled, although his revolutionary activism received continued admiration from younger socialists.

He gave a lecture titled Kärlek utan barn (Love without children) in Stockholm on 7 April 1910.

"The conservative newspaper Nya Dagligt Allehanda was outraged by Bergegren's speech and in an article published on 16 April 1910 the paper described it as "nasty propaganda".