Lomax, who starts in his new role this week, will lead the corporate comms agency's 10-strong team and oversee client work as it continues to grow, the firm said in a statement.
Lomax was part of the team that led the merger of Mandate, Hogarth and Penrose to form MHP Communications in 2010, and later became chief operating officer and managing director of MHP’s corporate affairs division.
Winn, who launched Blakeney in 2016 after his stint as director of external relations and senior business advisor for the Britain Stronger in Europe campaign, said: "Jonathan is one of the most experienced corporate communications consultants in the UK, and I’m delighted that he’s joining the Blakeney team.
"Jonathan’s strategic approach and experience working across complex and challenging client issues makes him a perfect fit for Blakeney, and I’m excited to be working with someone of his calibre as we continue to build on the success of our first three years."
Lomax said: "I have been incredibly impressed by what Blakeney has achieved in such a short time. The consultancy already represents a group of impressive clients, helping them deal with challenging and complex issues, and the quality of the work is first-class.
"I am thrilled to be joining Blakeney at this exciting time, and look forward to working with the team as we push forward into the next phase of growth."
Its clients have included Shell, Gatwick Airport, The Really Useful Group, and OVO Energy. Current clients include racing industry consortium Alizeti Group, venue operator The Madison Square Garden Company, and Oak View Group, an advisory and investment firm in the sports and entertainment industry.
The agency generated UK revenue of £1.4m in 2018 - its first full year of operation - up from £549,000 in 2017, PRWeek research previously revealed.