The actor, 38, was convicted of two misdemeanours for disorderly conduct and carrying a concealed weapon during a trial in May (15), after allegedly pulling a knife on Casey Smet in December (14).
Diamond, who denied the charges, claimed he acted in self-defence to protect his partner, Amanda Schutz, who was also found guilty of disorderly conduct.
Diamond returned to a Wisconsin court on Thursday (25Jun15), when Judge Paul Malloy ordered him to serve four months behind bars, insisting the sentence "has to send a message to the community that we're just not going to live like this".
The TV star was also placed on 15 months' probation. He must report to jail on Sunday (28Jun15).
Apologising for his actions during the hearing, Diamond said, "I sincerely apologise to everyone involved. This was the single most terrifying experience of my life... This is all I've been able to think about for the last six months."
Schutz, 27, was fined $500 (£313) for the disorderly conduct charge.
Diamond avoided a harsher sentence after he was cleared on a felony count of reckless endangerment.
Wil Wheaton, you've been a busy man! First there was that exhaustive work you...
"Swingers" lounge lizards Jon Favreau and Vince Vaughn are reunited in "Made" as a pair...