Mrs Cox was a regular visitor to the Ancienne Belgique concert hall, which backs onto the square, when she worked in the city before being elected to Parliament in 2015.
Mohamed Ouriaghli, a Brussels politician, said the square would be named after the late Batley & Spen MP on September 27.
He wrote on Twitter: “On 27.09 at 1pm, [Jo Cox] will have her name attributed to the place located at the back of the Ancienne Belgique, a place she frequented during her stay at #BXL.
“This event is in her honour and in the wish to feminise the squares and street names of the @VilleBruxelles.”
News of the tribute was welcomed by Mrs Cox’s sister, Kim Leadbeater, who will be attending the naming ceremony with her parents, Jean and Gordon.
She said: “We are honoured that the city of Brussels has chosen to remember Jo in this way.
“She had many happy times living there and made some deep and long lasting friendships.
“We visited her on several occasions and have many heartwarming memories of seeing how much she enjoyed being there.
“To know that she will have a permanent place where she will be remembered is a comfort and an honour and I would like to thank everyone involved.”
The announcement was also welcomed by Stephen Kinnock, MP for Aberavon, whose mother, the former MEP Glenys Kinnock, employed Mrs Cox as an assistant in Brussels.
He tweeted: “What a lovely gesture. Jo loved living in Brussels, and back in the day we all loved going to the Ancienne Belgique – a fantastic live music venue. Kudos and ‘un grand merci’ to the City of Brussels, for doing this.”
Mrs Cox, a 41-year-old mother-of-two, was killed in Birstall, near Batley, by neo-Nazi fanatic Thomas Mair in 2016.