Takeaway bosses Mohammed Abdul Kuddus, 40, and Harun Rashid, 38, have been found guilty at Manchester Crown Court of the manslaughter by gross negligence of Megan Lee, 15, who suffered an allergic reaction after ordering food from the Royal Spice in Oswaldtwistle, Lancashire.
The jury at Manchester Crown Court also found Rashid guilty of failing to discharge a general duty of employers, contrary to the Health and Safety at Work Act, and another count of failing to put in place, implement and maintain a permanent procedure or procedures in contravention of European Union food safety regulations.
Kuddus had already pleaded guilty to those two charges on behalf of himself and of behalf of the Royal Spice Takeaway Ltd.
The trial heard Megan suffered an allergic reaction to food ordered from the Royal Spice, in Oswaldtwistle, Lancashire, on December 30 2016 and died two days later.
Megan's friend ordered through the Just Eat website and wrote "prawns, nuts" in the comments and notes section, but the meal was later found to have the "widespread presence" of peanut protein.
Her family were in tears in the public gallery as the verdicts were read out on Thursday afternoon.
Judge Mrs Justice Yip bailed both men until November 7, when they and the company will be sentenced.
She said: "The fact that I am granting bail shouldn't be taken as any indication there should be a non-custodial sentence.
"You need to prepare yourselves for a custodial sentence."
Kuddus and Rashid made no comment as they were approached by media while leaving court following the verdicts.