Peter Madsen was found guilty in April of murdering and mutilating 30-year-old Kim Wall on the craft in Copenhagen harbour in 2017.
He had not appealed against the conviction, therefore the Eastern High Court only ruled on the decision to give him a life sentence - which typically lasts for around 15 years in Denmark.
Wall was interviewing Madsen for the US magazine Wired on the inventor's race against another Danish group to be the first to send a person into space in a home-made rocket, her boyfriend said during the April trial.