The so-called rainbow runabout from the World Cup match between Portugal and Uruguay (2-0) is free again.
The Italian was released after a brief arrest, the Italian Foreign Ministry said on Tuesday.
The man, now identified as 35-year-old Mario Ferri, apparently does not have to fear any further consequences.
"The Ministry of Foreign Affairs has been following the case together with the Italian embassy in Doha," the ministry told the AFP news agency, without giving any further information on the man's whereabouts.
"After a short arrest, the man was released by the authorities without further consequences."
Ferri ran onto the pitch early in the second half and was on the pitch for around 30 seconds before being led away by security guards.
Alongside a rainbow flag, he wore a T-shirt with the words "Save Ukraine" on the front and "Respect for Iranian Woman" on the back.
The tournament in Qatar is one of the most controversial in the history of the World Cup, mainly because of the human rights situation in the Gulf Emirate.
Among other things, homosexuality is a punishable offense in Qatar.
Ferri is no stranger to his homeland: he was arrested in Abu Dhabi at the end of 2010 when he stormed the pitch at the Club World Cup final – with the message “Free Sakineh” on his shirt, based on an Iranian woman who threatened with the death penalty by stoning.
At the 2014 World Cup in Brazil, he ran onto the pitch during the match between Belgium and the USA with the words "Save the children of the favelas" written on his Superman shirt.
Most recently, he helped women and children from Ukraine to flee to Poland. As a footballer, he played for SP Tre Fiori from San Marino in the Conference League, among others.