The move is part of a £9m investment into the business by capital investor BGF.
Triangle Fire Systems specialises in the design, installation, and maintenance of sprinkler systems in domestic, commercial and retail buildings across the UK.
The firm has a particular focus on residential developments and high-rise apartments and has delivered consistent growth with revenue in excess of £21m in 2020.
The investment from BGF will enable Triangle Fire Systems to expand its team of 100 specially trained staff and establish new service lines.
The business will also look to pursue a targeted buy and build strategy to complement its organic growth.
Castle joins as part of the deal following an introduction from BGF’s Talent Network – the largest pool of non-exec talent in the UK and Ireland.
Castle stepped down as Mace COO last April after 16 years in the role. He is currently a None Executive director at Mace and Eleco.
Colin Chantler, CEO at Triangle Fire Systems said: “We are delighted to announce the new funding from BGF and the appointment of Mark Castle to the board.
“The investment, alongside Mark’s unparalleled experience will help us grow our reach and expand our services across the residential and commercial property market.
“As a family-run enterprise, it was important to us that our investor understood this dynamic, and BGF’s track record of successfully scaling family run businesses means that we can continue to grow in a way that works for us.”
Castle added: “I look forward to putting my experience of scaling businesses to good use as the company gears up for its next stage of growth.”