Williams, avoiding a retrial on a reckless manslaughter count that deadlocked the jury at his 2004 trial,in the death of Costas Christofi on Feb. 14, 2002. At the same 2004 trial, he was acquitted of aggravated manslaughter but convicted on four counts of covering up the shooting.
The sentences on the assault and cover-up counts will run concurrently. State Superior Court Judge Edward Coleman went along with a plea agreement that spelled out the five-year prison sentence and the potential for Williams to be released as early as summer 2011.
In court Tuesday, a tearful Williams turned and apologized to Andrea Adams, Christofi's sister, saying, "There's not a day I wake up that I don't feel sorry for what I did to Mr. Christofi and that I put you through this."
Adams wrote in a letter read by a court employee that the punishment "didn't fit the crime" and spoke of "eight years of agony watching Jayson Williams prance around and live his life and acting like nothing happened."
Williams paid Christofi's family more than $2 million in 2003 to settle a wrongful death lawsuit.
Williams had been free on bail since being charged in 2002, but was taken from the courtroom in handcuffs to begin serving his sentence.
On the night of the shooting, the 55-year-old Christofi had driven Williams and several of the basketball player's friends to Williams' mansion after taking them to a local restaurant.
Williams said at his plea hearing last month that he gave the group a tour of the house and showed them his gun collection in his bedroom. While showing off a double-barreled 12-gauge shotgun, Williams admitted, he failed to check the safety mechanism and inspected only one of the two barrels before snapping it shut.
The gun fired, striking Christofi once in the chest and killing him. Witnesses testified that Williams tried to cover up his involvement by initially placing the gun in Christofi's hands and instructing those present in the bedroom to lie about what happened.
"Had the defendant exercised one ounce of caution that night, Gus Christofi would still be alive and we wouldn't be here," Deputy Attorney General Steven Farman said Tuesday.
The legal wrangling in the case eventually took on a life of its own, beginning with a change of venue for the trial from Hunterdon County, the site of the shooting, to Somerset County.
In 2007, defense attorneys tried to get the case tossed out after Hunterdon County Prosecutor J. Patrick Barnes divulged that a white investigator in his office had used a racial slur to describe Williams, who is black, in a 2002 meeting. The dispute reached the state Supreme Court, but Coleman refused to throw out the 2004 convictions or the retrial.
Williams, who turned 42 on Monday, played nine seasons with the Philadelphia 76ers and New Jersey Nets before a leg injury forced him to retire in 2000. He was in the second year of a six-year, $86 million contract.
Known for his gregarious personality, Williams became an NBA analyst for NBC but was suspended after Christofi's shooting. He attempted a short-lived comeback in the minor league Continental Basketball Association in 2005.
Williams has suffered several recent personal setbacks.
His wife filed for divorce last year, but has attended his recent court appearances and was in court Tuesday.
Police used a stun gun on him in a New York hotel last year after a female friend said he was acting suicidal. He was charged with assault in May after allegedly punching a man in the face outside a North Carolina bar, but charges were dropped. His father, E.J., with whom he owned a construction business, died in South Carolina in November.
Last month he was charged with drunken driving after he crashed his SUV in Manhattan. Prosecutors said his blood alcohol level was more than twice the legal limit.
"To my family, please forgive me for the pain I've caused you," Williams said Tuesday as he read from a statement. "You deserve a better father, a better brother and son than I have been. I am not a bad man, but I acted badly on Feb. 14. I will work endlessly to improve myself and make positive contributions to society."