The agency, which officially launched this week, offers PR support for "living" businesses - meaning property, interiors, and health-and-wellness brands.
Thomas spent almost seven years at Luchford between 2010 and 2017, prior to which she spent four years as associate residential PR manager at estate agents Knight Frank.
Her fellow co-founder Harwood-Smith, who served as an account manager at Luchford between 2010 and 2011, said Maison Communications was born of "a genuine energy to create something a little different".
Prior to co-founding Maison, Harwood-Smith worked on a freelance basis. Several of her clients, including Humberts, First Home, Haringtons and Vita Mojo, now work with Maison Communications.
She said: "It felt like there was a real gap for a PR business that focused not just on property and interiors, but the main elements associated with 'living' such as health and wellness. Nowadays our clients want to partner with like-minded brands and influencers who both inspire and connect with their existing target audiences.
"Now is the time for us to propel standard property PR into a wider ‘living’ sphere and maximise on exciting UK and global opportunities."