[1] Dahl was born in Melhus Municipality in Søndre Trondhjem county, Norway.
He was the son of Nils Nilssøn Dahl (1806–1854) and wife Christopha Kirstine Rønneberg (1812–1890).
[4] He was a strong proponent of the impeachment of Prime Minister Christian August Selmer in 1883, and received national attention for his role as a prosecutor in the trial.
Later the same year, he was made Minister of Justice, but remained there only for a few months, since the cabinet had to resign in June 1889.
[7] Dahl later wrote a three-volume biography on Prime Minister Johan Sverdrup titled Johan Sverdrup; et storthingsbillede (Det Norske aktieforlag, 1899).