Los Angeles Superior Court Judge John S. Fisher imposed the maximum term allowed against Chidi Benjamin Uzomah Jr. as a result of his March 9 plea.
The judge also issued a protective order that requires Uzomah to stay 500 yards away from Seacrest and his workplace for 10 years, according to Deputy District Attorney Wendy Segall.
Local news from across Southern California
"This is a very difficult situation for people when they're stalked," the judge said.
Fisher noted that Uzomah was on probation at the time of the crime last Oct. 30 -- for a confrontation about 1 1/2 months earlier with a security officer assigned to protect Seacrest after a charity event at Children's Hospital of Orange County -- and said state prison was the appropriate punishment for the latest offense.
The judge's ruling followed a 90-day psychiatric evaluation by state prison officials.
Two misdemeanor charges against Uzomah -- disobeying a court order and attempted disobeying of a court order -- were dismissed as a result of his plea.
Los Angeles police Detective Rosibel Smith, of the LAPD's threat management unit, testified at a Jan. 19 hearing that Seacrest told her he was "very intimidated by Mr. Uzomah's presence, by his size" after being informed that the 6-foot-4 inch, 200-pound defendant had shown up to see him at the E! building in the 5700 block of Wilshire Boulevard.
"He was very much in fear of him," Smith testified of Seacrest's reaction, noting that Seacrest knew Uzomah had been carrying a knife when arrested following his September 2009 encounter with the defendant at the Orange County event.
Seacrest recalled that Uzomah demanded an autograph from him -- a request with which he complied -- then stepped up and blocked his path until security intervened and pushed him in a waiting car to keep him away from the defendant, Smith testified.
According to the detective, Seacrest said he looked in his rear-view mirror and saw Uzomah involved in a physical confrontation with a security officer.
Uzomah also had a pocketknife with him when he was searched after his Oct. 30 arrest at the E! building, the detective testified at the hearing in January.
Seacrest said he was also informed that Uzomah came to the KIIS-FM studio in Burbank last Oct. 2 to look for him, Smith testified.
The detective noted that Uzomah's probation conditions for the Orange County run-in required him to stay away from Seacrest and Children's Hospital and not to own, use or possess any dangerous or deadly weapons.
Seacrest's attorney, Blair Berk, told reporters outside court, "Ryan is extremely appreciative of the work of the Los Angeles County District Attorney's Office in this matter."