More than 100 protestors gathered at the Exhall interchange near Coventry, placing traffic cones and blocking the southbound carriageway near Junction 3, causing a complete blockage of the lanes to Junction 2.
Those taking part in the march were seen holding placards and chanting 'Black Lives Matter' as they walked down the motorway lanes at 5pm on Sunday.
The protest was in solidarity with other Black Lives Matter campaigns held over over the weekend in the Midlands, following the death of George Floyd in America.
One motorist said the crowd blocked off the road with cones before police arrived to manage the traffic, while another described being stuck for more than an hour as the protest took place.
Another eye-witness, who asked not to be named, described how they had to stop as the protestors just appeared in the road.
They said: "I was going 70mph then they just walked out into the road in front of me.
"They put traffic cones down and then sat down. I’d say there are 100 here. They came on at junction 3 of the M6 and now there’s a rolling roadblock to junction 2.
“The traffic has been held both sides. The police helicopter is up and there is a police dogs team here as well. The group were chanting ‘Black Lives Matter’ over and over again."
Motorists were urged to avoid the area near Junction 3 and find alternative routes during the protest, which last around two hours until the protestors headed off the motorway into Coventry.
The M6 was fully reopened just after 8pm.
It followed protests across the country, including in Wolverhampton where around 1,000 people gathered in West Park.
The Prime Minister said demonstrations had been “subverted by thuggery” after protesters tore down a statue of a slave trader in Bristol and clashed with police in the capital.
Scotland Yard said 12 people were arrested and eight officers injured as bottles and other objects were thrown in central London on Sunday.
Graffiti was scrawled on the statue of Sir Winston Churchill in Parliament Square, while in Bristol protesters toppled the bronze memorial to slave trader Edward Colston and dumped it into the harbour.