The 54-year-old was convicted of two counts of common assault against the boys, aged 14 and 15, in a food store in north London, in October 2014.
One boy had been trying to pass Joyce in a narrow aisle and after an exchange of words was knocked to the floor.
Joyce will be sentenced at Westminster Magistrates' Court on 27 May.
The former Labour MP had claimed he was performing a "citizen's arrest" at News & Food Express in Chalk Farm and asked the shopkeeper to call police.
The attack happened close to the drinks fridge at about 21:40 BST on 17 October and was filmed on the store's CCTV.
Joyce "flung" the 14-year-old boy to the floor and held him down by the throat, the court heard.
"He started shouting in my face. I remember begging him to leave me alone," the boy said.
His 15-year-old  friend was elbowed and winded while trying to help and both boys then fled the shop, the court was told.
Shopkeeper Ali Fahan said: "I told the man to let him go because he was crying."
Giving evidence, Joyce insisted he had overcome his battle with alcohol after a string of previous convictions.
The court heard that he assaulted politicians in the House of Commons bar in 2012, which led to his resignation from the Labour Party.
He said: "I have a background as a judo player. I was conscious I didn't want to over-act."
The former army major told the court he felt threatened when the boys walked by because one was shouting and swearing and had taken an "aggressive" stance.
Joyce said he put his hand out to stop the teenager knocking over a supermarket shelf but it fell anyway.
Delivering his verdict, District Judge John Zani said: "In my view, you underplayed the violence you meted out to these young men and wanted the police called so as to justify your actions.
"You readily told police, incorrectly, that [one boy] head-butted you for no reason."
He said all sentencing options including imprisonment would be considered.
Joyce is not standing in the general election and has been released on conditional bail until sentencing.
Former Falkirk MP Eric Joyce has been found guilty of assaulting two teenage boys in an "unjustified and unprovoked" attack in a shop.