A jury found Shawn Laval Smith, 34, guilty of first-degree murder with a special circumstance.
Smith faces a maximum sentence of life in prison without the possibility of parole.
The day before the verdict was read, Kupfer's family and loved ones filled a courtroom for closing arguments in the trial against Smith.
"He used her kindness against her," said Habib Balian, Los Angeles County Deputy District Attorney. "He then slayed her... When he was close and he was safe and her guard was down...left her bloody on the floor."
Prosecutors sought to persuade the jury to find Smith guilty of first degree murder, arguing that he premeditated killing of the 24-year-old.Kupfer was working alone in a furniture store on La Brea Avenue in January 2022 when she was stabbed to death.
"With this filet knife, penetrated her body - punctured lung, punctured stomach, punctured liver," said Balian.
Balian said recordings left behind by Smith, which included audio of Kupfer's killing, show Smith was motivated by a desire to kill women.
Trial begins in brutal slaying of UCLA student Brianna Kupfer in Hancock Park store
On Monday, the defense did not argue Smith was innocent. His attorney stressed some of the recordings from about two weeks before Kupfer's killing showed rants against men and women - not a motive.
"The dude was expressing his tantrum to himself, it sounds like he was blowing off steam, probably because he was pissed off about something in that moment. Who the hell knows what it was?" said Rober Haberer, Smith's defense attorney.
The defense also challenged a first degree murder charge, arguing the killing was not premeditated.
"The decisions to attack Brianna Kupfer happened in an instant. To say that the perpetrator engaged in something like reflective contemplation is ludicrous," said Haberer.
Over course of the trial, several witnesses took the stand, including responding police officers. The prosecution also pointed out Smith's DNA was found on the handle of a knife with Kupfer's blood, the sheath that covered it, and the audio recorder.