The singer put forward versions of the pieces Kissing Coppers, Girl with Balloon and Vandalised Oils (Choppers) from his personal collection for bidding in January.
The auctioneers, Sotheby’s, sold two of the works on Wednesday (2 March).
Vandalised Oils (Choppers), which is understood to have an “anti-war” message, went for just under £4.4m. Its initial estimate stood between £2.5m and 3.5m.
Girl With Balloon fetched £2.8m, after being priced at £2m to £3m.
Williams first acquired the painting directly from Banksy in 2006. However, the graffitied image made its debut under Waterloo Bridge in London in 2002.
Both of the recently sold pieces are some of the anonymous street artist’s most recognisable works.
Girl With Balloon is particularly famous as a canvas version of the piece was shredded at an auction in 2018, immediately after it sold for £1m.
“These works unite the cultural legacies of two of Britain’s biggest stars: Robbie Williams and Banksy,” said Hugo Cobb of Sotheby’s at the time of their initial auction listing earlier this year.
“Like their creator and like their owner, they are acerbic, iconic, irreverent and unique.”