Demonstrators echoed the unarmed black man's last words as they vented their anger at a decision not to charge a white policeman over his death.
“I can’t breathe”, chanted the protesters in New York’s Grand Central Station.
The words were Eric Garner’s last, repeated several times as he was held down by police.
People rallied at several locations in New York and other American cities as far away as Seattle – angry at a grand jury’s decision not to charge a white officer for causing an unarmed black man’s death with a “chokehold”.
It’s the second case in a week to highlight questions of race and justice in the US.
The nationwide protests reflect widespread anger at the policing of minorities.
Garner, 43, was tackled on Staten Island in July by police who accused him of illegally selling cigarettes.
“It’s dead wrong, he’s a murderer, a cold blooded murder… That’s it, homicide, it’s a homicide,” shouted furious Staten Island resident Jenny Chambers.
“To kill that man over here over a loose cigarette which costs 50 cents, to choke him, to have him saying that ‘I can’t breathe’, you have video and you have audio and you can’t get a conviction, what else do you need?” asked a male resident.
Police claim Garner resisted arrest.
The officer, named as 29-year-old Daniel Pantaleo, has testified that he did not intend to choke Garner and never thought he was in mortal danger.
The confrontation was caught on video and has circulated widely on the internet.
The US Justice Department is investigating whether the dead man’s civil rights were violated.
The alleged chokehold is a banned police restraint.
The medical examiner in New York called the death a homicide, saying officers had killed Garner by compressing his neck and chest, adding that his asthma and obesity were contributing factors.