Ian Tomlinson was unlawfully killed by a Metropolitan Police officer at the G20 protests, an inquest jury has said.
The 47-year-old collapsed and died after he was hit by a baton and pushed to the ground by Pc Simon Harwood at the protests in London on 1 April 2009.
His family said the verdict was a "huge relief", while the Crown Prosecution Service could reopen criminal proceedings against Pc Harwood.
The officer said after the verdict he had not intended to push him over.
The jury decided Pc Harwood acted illegally, recklessly and dangerously, and used "excessive and unreasonable" force in striking Mr Tomlinson.
Jurors added that the newspaper seller, who was not taking part in the protests, posed no threat.
The case is set to be reviewed by the Crown Prosecution Service (CPS) and the Met Police.
Pathologist Dr Freddy Patel told the inquest that Mr Tomlinson died of a heart attack but the jury favoured the evidence of a number of experts who said he died of internal bleeding.
During evidence, the family's lawyer Matthew Ryder QC said Pc Harwood had told "half truths" and "deliberately painted a false picture of Mr Tomlinson".
Outside the hearing, Mr Tomlinson's step-son Paul King said the family hoped manslaughter charges would be brought against Pc Harwood.
Mr King said: "After two years, we're really grateful that the inquest process has made a strong statement about how Ian died.
"We are grateful to the jury and the coroner and we think the jury finding speaks for itself in the verdict of unlawful killing."
Last year, prosecutors said a decision not to pursue charges against Pc Harwood could be reviewed depending on the inquest findings.
Jurors took four-and-a-half hours to reach their verdict. The other possible verdicts available to them were misadventure, natural causes and open.
Jules Carey, of the Tomlinson family's solicitors, said: "Today's decision is a huge relief to Mr Tomlinson's family.
"To many, today's verdict will seem like a statement of the blindingly obvious; however this fails to take account of the significant and many obstacles faced by the family over the last two years to get to this decision.
"The CPS will now review whether a prosecution will be brought following today's verdict and the way in which the evidence has been clarified during the inquest process."
The CPS said a "thorough" review would take place.
A spokesman said: "It will take into account all of the evidence now available, including any new evidence that emerged at the inquest, the issues left by the coroner to the jury and the conclusions they reached.
"The review will be conducted as quickly as is compatible with the care and rigour required in a thorough exercise."
The Independent Police Complaints Commission (IPCC) said it acknowledged the verdict and would be publishing various reports on the incident.
Speaking after the verdict, Deputy Assistant Commissioner Rose Fitzpatrick of the Met Police said: "It is a matter of deep regret that the actions of an MPS [Metropolitan Police Service] officer have been found to have caused the death of a member of the public."
The Met said Pc Harwood would be the subject of misconduct proceedings.
Pc Harwood disputed the jury's verdict that he deliberately and intentionally shoved Mr Tomlinson to the ground.
A statement released by the officer's lawyer said: "The mass of video and other evidence gathered by the IPCC now presents a picture very different from the one which Pc Harwood had on the day.
"In particular, he wishes that he had known then all that he now knows about Mr Tomlinson's movements and fragile state of health.
"Pc Harwood did not intend, or foresee at the time, that his push would cause Mr Tomlinson to fall over, let alone that it would result in any injury."