Company veteran Blowers steps down with immediate effect after 26 years at ISG, and the last two years serving as chief executive.
He will be followed out of the door by finance director Karen Booth, who has also been with the firm for 5 years, and will step down in March.
The top-level shake-up at the £2.2bn turnover contractor will see chief operations officer Zoe Price become new chief executive, with Andrew Page brought in as interim chief financial officer.
Price’s 12-year career at ISG includes other previous roles as group director for public sector frameworks and COO for UK Construction.
She said: “I’d like to pay tribute to the contribution that both Matt and Karen have made to the ISG business.
“We have not been immune to the challenging landscape of the construction industry over the past few years, but our focus on collaboration and quality delivery, alongside our investment in our people have characterised this period.
“Looking forward, I’m determined to build on this legacy, but also seek to more fundamentally reset how our business, and the wider industry responds to the growing challenges to our sector.”
The top-level departures come as several other directors are understood to be in the process of leaving ISG.