The activists threw tomato soup at the Sunflowers owned by the London Gallery - the painting targeted two years ago - and another from the series that is on loan from Philadelphia Museum of Art for a temporary exhibition.
The National Gallery said three people had been arrested and the paintings were unharmed.
The stunt came just a few hours after Phoebe Plummer, 23, and Anna Holland, 22, were sentenced for throwing tins of tomato soup on the London-based artwork in October 2022, before gluing themselves to the wall below the painting.
The soup caused up to 10,000 pounds ($A19,385) worth of damage to the frame in 2022, prosecutors said, although the painting – which was behind a protective screen – was unharmed and went back on display later the same day.
Plummer and Holland pleaded not guilty but were convicted after a trial at London's Southwark Crown Court, where Plummer was sentenced to two years in prison for the criminal damage charge.
Holland was sentenced to 20 months in prison.
Judge Christopher Hehir told Plummer and Holland: "You two simply had no right to do what you did to Sunflowers, and your arrogance in thinking otherwise deserves the strongest condemnation."
Plummer said she took part in the protests knowing she could be arrested and jailed, saying she was being made a political prisoner, which the judge said was ludicrous and self-indulgent.
"It is offensive to the many people in other parts of the world who are suffering persecution, imprisonment and sometimes death for their beliefs," Hehir said.
Plummer was also sentenced to an additional three months in prison on Friday, having been separately convicted of the relatively new offence of interfering with the use of key national infrastructure.
Friday's sentencing comes amid a wider crackdown on protest movements in the United Kingdom and across Europe.
Activists from Just Stop Oil have staged a number of eye-catching protests in recent years and five members of the group were jailed in July for at least four years for a conspiracy to block London's M25 motorway, in the longest sentences ever imposed for a non-violent protest in the UK.
