The National Audience, Spain's top criminal court, found Cassandra Vera, 21, guilty of glorifying terrorism and humiliating victims of terrorism and slapped her with a one-year jail term.
She is unlikely to spend time behind bars though as offenders of non-violent crimes with a sentence of under two years do not serve time in jail.
Vera published 13 tweets between 2013 and 2016 about the assassination of Admiral Luis Carrero Blanco, the prime minister and heir apparent of dictator Francisco Franco who was killed in a car bomb attack in Madrid on December 20, 1973 carried out by the Basque separatist group Eta.
The massive explosion sent the car Carrero Blanco was travelling in hurtling into the air and over the roof of a church where he had just been attending mass.
"Eta combined a policy against the use of official vehicles with a space programme," read one of the posts. Another said: "Did Carrero Blanco also go back to the future with his car?"
The case has raised questions over freedom of expression in Spain and Vera has received much support. The leader of far-left party Podemos, Pablo Iglesias, accompanied her to her trial.
Even the granddaughter of Carrero Blanco attacked the move by public prosecutors to charge and put Vera on trial, saying in a letter sent to daily El Pais in January that while the jokes were in poor taste they were not worthy of such legal action.
"I'm scared of a society in which freedom of expression, however regrettable it may be, can lead to jail sentences," Lucia Carrero Blanco wrote.