The weapon, a Bruni Olympic pistol which the jury decided unanimously was being carried by Duggan, was found on grass behind a fence some 6m away from where he fell with bullet wounds to his arm and chest.
The jury had heard evidence from the police marksman who fired the shots, known only by his call sign of V53, that he had seen the father of five levelling a gun, hidden in a sock, towards him as he pulled the trigger on his weapon.
Jurors were reminded by the coroner, Judge Keith Cutler, that they could never disclose their deliberation. But it seemed clear they had found that in the chaos of the early evening of August 4, 2011, V53 had acted in self-defence or the defence of others in the "honest belief" that Duggan posed a threat to the lives of those around him.
The conclusion that Duggan had nonetheless disposed of his weapon before shots were fired by police visibly convulsed his family.
In extraordinary scenes, his brother Marlon, with whom Mark Duggan had been talking on the phone moments before his death, leaped to his feet after the findings and shouted towards the jurors. A family supporter also shouted: "Murderers. A black life ain't worth nothing."
Pamela, Duggan's mother, appeared to pass out in court before being later helped from the room.
Speaking outside the court, Carole Duggan, said: "The majority of the people in this country know that Mark was executed. We are going to fight until we have no breath left in our body for Mark and his children."
The family's solicitor Marcia Willis Stewart said: "On August 4, 2011, an unarmed man was shot down in Tottenham. Today we have had what we can only call a perverse judgment. The jury found that he had no gun in his hand and yet he was gunned down. For us that's an unlawful killing."
In an attempt to dispel the fog of claim and counter-claim surrounding the shooting, the Yard said it would now introduce cameras to be worn by its armed officers in the coming months to record their actions during operations.
Police said that in nearly 13,000 incidents in which firearms specialists had been deployed between 2010 and 2012, shots had been fired on four occasions.
A vigil for Duggan will be held outside Tottenham police station on Sunday.
- Independent