The brand, which specialises in ‘burgers and bubbles’, has ceased trading at its bars in Wandsworth, Brixton and Camberwell.
Grand Union’s five other sites in Camden, Chancery Lane, Farringdon, Kennington and Paddington are to remain open.
The sale comes after the group revamped its food offering to offer 'Italian American diner fare' such as burgers, pizzas and barbecue ribs and wings to share.
BigHospitality’s sister site MCA reported in December that the bar group, which is backed by Patisserie Holdings and 3Sixty Restaurants part-owner Luke Johnson, was reviewing its options for a sale.
A statement on Grand Union’s website said: “After 10 amazing years Grand Union has taken the decision to sell three of our venues.
“As of 22 May 2017 Grand Union Brixton, Camberwell and Wandsworth will no longer be part of the the Grand Union group. We would like to thank our beautiful, happy and loyal customers for their support over the years.”
Grand Union was founded in Camden in 2006 by Marshall and Adam Saword. The latter sold his 50% stake to Johnson in 2013.