Chidi Benjamin Uzomah Jr., 26, received the maximum sentence after previously pleading no contest to stalking. Uzomah did not speak during the sentencing hearing.
Superior Court Judge John S. Fisher rejected a defense request to sentence Uzomah to probation.
"The court feels state prison is warranted," he said.
The judge also issued a restraining order requiring Uzomah to stay 500 yards away from Seacrest and his workplace for 10 years.
"Ryan is extremely appreciative of the work of the Los Angeles County District Attorney's office in this matter," his attorney Blair Berk said after the hearing.
Uzomah has been jailed since his arrest in October at E! Entertainment Television studios in Los Angeles, where he tried to reach Seacrest.
Court filings state he was carrying a knife.
Uzomah was on probation at the time for an incident in Orange County, Calif., in which he eventually pleaded guilty to three misdemeanors, including assault, battery and carrying a switchblade knife after he attacked one of Seacrest's bodyguards outside an event.
