Sam Lutfi, who is suing Spears' parents for defamation, testified while they watched from across the courtroom.
He denied accusations made in a book by Lynne Spears that he was a Svengali who became the gatekeeper of her daughter's world, locking her parents out of her life.
He contends he was a benevolent caretaker who protected Britney during her highly publicized meltdown.
Lutfi's direct testimony concluded in dramatic fashion as he was overcome by tears while describing the aftermath of the publication of the book.
"After the book came out, there was a huge spike of death threats that were pretty bad," he testified. "People I know were shunning me. Websites were created to kill me. People wished I was dead. People wished my family ... "
He didn't finish the sentence because he was crying.
"How did it make you feel," asked his attorney, Joseph Schleimer.
"Depressed, anxious and suicidal," Lutfi testified.
Lutfi told of days leading to Britney's hospitalization at a psychiatric unit, and jurors saw a video of the star ordering him around outside her home hours before she was taken away.
She was demanding that he let her drive her car and told him to get in the passenger seat. The scene outside her home was surreal, with TV lights and paparazzi surrounding her.
Lutfi said Britney feared her father Jamie Spears and fled her home when she heard he was coming. Lutfi said the father confronted him twice and punched him on the second visit.
"Jamie came barging into the house. He lunged at me and chased me around the kitchen island. He was spitting, yelling, shouting at me, and said I had hurt his daughter and he was going to beat the hell out of me and I'd better get out of the house," Lutfi testified.
After 10 minutes, he said, Jamie Spears was escorted out by security guards. But the next morning, he got into the house again and the battle resumed, Lutfi said.
"He cornered me in the kitchen, punched me in the solar plexus and threatened to kill me," Lutfi testified.
"How did it feel?" Schleimer asked.
"It hurt," Lutfi replied.
Asked what he did, he said, "I ran to the game room and locked myself in."
A lawyer for Spears said in opening statements that the father never physically assaulted Lutfi and merely touched him on the chest.
With Schleimer reading excerpts from Lynne Spears' book, Lutfi methodically denied every one of her accusations.
"Were you in complete control of Britney's life?" Schleimer asked.
"No," Lutfi said firmly.
"Did you attempt to keep Britney's family away?" he was asked.
"To the contrary, sir," Lutfi answered.
He denied cutting wires to phone lines in the house and hiding Britney's cellphones. He also said he never drugged the superstar.
Lutfi was expected to undergo cross-examination later in the day.
He is suing for damages for defamation and for a 15 percent share of the millions of dollars Britney made while he was with her.
The singer remains under the conservatorship of her father and has been told by a judge not to attend or testify in the trial.
She has made a remarkable comeback from her hard times, now acting as a judge on TV's "The X Factor."