The demonstrators are demanding a firm start date for the delayed scheme despite mainly being made-up of anti-capitalists.
Bradford West MP Galloway is backing the Occupy Westfield movement and has visited the site which currently contains around 40 protesters.
They are refusing to leave the site until a construction start date is set for the job where work first began in 2004 but stopped in 2008 leaving an empty site in the city centre.
Campaigners are refusing to budge until a construction start date is agreed.
Westfield won revised planning permission for a smaller £275m scheme in October but little progress has been made on site since.
Galloway told the Yorkshire Post: “I wholeheartedly support the occupation of the site as a way of drawing attention to the failure of this council and the developers to even lay one brick there, and as a way of putting pressure on both of them either to start the development or get out of the way and allow others with fresh ideas to take over.”
Westfield has told the campaigners: “We appreciate your concerns but would like to reassure you that Westfield remains committed to progressing the scheme and is currently undergoing detailed negotiations to secure retailers as well as other important predevelopment activities which by their nature are not physically evident on site.
“Westfield has safety concerns as you are currently trespassing on a construction site. By entering and occupying the site, you are not only endangering yourselves but also others.
“The site needs to be properly secured and managed to avoid the very real possibility of injury both to you and the wider Bradford public. We urge you to leave the site immediately so that we can secure it and remove the risk of accidents.”