Ellis joins the PR firm from Atomic, where she was a director overseeing a team of 25 working across consumer, B2B and technology clients.
At Lewis, she will oversee various accounts and drive the agency's integrated marketing offering, the agency said. Her experience in this area spans 25 years working for brands including British Airways, Dell, Pernod Ricard and Skype.
Holmes is joining Lewis to head a number of technology and B2B accounts. He joins from Limelight PR, where he was most recently managing director UK and before that founded its Middle East office. Holmes has been charged with developing Lewis's professional services and fintech clients.
Lastly, Uppal is returning to Lewis as an associate director, having spent a year out in Dubai. She joined Lewis in 2012 from Text 100 in India.
Giles Peddy, Lewis's senior vice-president, EMEA operations, and its UK managing director, said: "The agency has set itself an exciting vision for the next few years and having the ability to invest in such talent gives us the platform to continue to deliver great work, support our people and develop the agency to meet the needs of our clients now and tomorrow."
Lewis said it generated $62m in revenue for the year ending July 2017 and a profit of $8m. New wins contributing to its 23rd consecutive year of growth included Comcast, Google, Jabra, LG, McAfee, Porsche and Wix.com.