Furness made his grand slam main draw debut at the 2018 French Open, where he received a wildcard into the mixed doubles event, partnering Fiona Ferro.

In October 2017 he secured his first win over a top 100 player when he beat Marcos Baghdatis at the Eckental Challenger.

[6] In April 2022, he won his first Challenger tournament, as a qualifier, at the Ostrava Group Open, defeating Ryan Peniston in the final.

[7] In September 2022, Furness made his debut on the ATP Tour at the 2022 Moselle Open in Metz, France entering the main draw as a qualifier and losing in the first round to Alexander Bublik.

[citation needed] He was coached by his father Mark in Brittany before moving to the French Federation in Paris and he has a sister called Lucy.