During her 17 year tenure for a leading auction house, Sudlow worked on the most prestigious and high-profile single-owner auctions to come to market in that time including The Collection of the Late Mrs. T.S. Eliot, The Private Collection of President and Mrs. Ronald Reagan, The Joan Rivers Collection, Betsy Bloomingdale: A Life in Style, The Paul Walter Collection, The Peggy and David Rockefeller Collection, The Private Collection of Jayne Wrightsman, The A. Jerrold Perenchio Collection, Hubert de Givenchy: Collectionneur and The Ann and Gordon Getty Collection, amongst many others.

Gemma began auctioneering in 2012 and has set or broken numerous world auction records in the Books, Post War and Contemporary Art, Sculpture and Furniture & Works of Art categories. In 2019 she presided over the most valuable collection of musical instruments ever sold at auction with The David Gilmour Guitar Collection.

In 2021 she was the auctioneer for the first “white glove” (all lots sold) various owner contemporary art evening sale in New York in over a decade delivering 10 new world auction records in one night. She sold more lots than any other auctioneer globally for a leading auction house in 2021 with a sale total in excess of $500 million.