The judge, Adenike Coker, on Thursday found the convict guilty of manslaughter.
The verdict is coming three years after Mr Johnson, who was 36 at the time, was shot during a raid by a police officer at Onipetesi in Lagos, while watching the English premiership match between Tottenham and Manchester United on 31 March 2019.
The police officer wore a polo shirt with the Special Anti-Robbery Squad (SARS) inscribed on it.
The incident sparked outrage on social media and the police officer was dismissed, while Godwin Orji, a sergeant, who was also tried alongside the killer cop, was demoted.
Delivering judgment, Mrs Coker found the former inspector guilty of killing Mr Johnson and sentenced him to life imprisonment.
The convict was initially charged with murder, but the court found him guilty of manslaughter as a result of a lack of intention on his part.
The judge also held that the convict will be eligible for parole after serving a minimum of 25 years in prison.