McDowell has spent more than 30 years in the reinsurance market and was most recently CEO of Gallagher Re Bermuda.
Prior to that, he worked at Aon Benfield as CEO of Global Re Specialty in Bermuda.
Binetti joins the business from Everest Re Bermuda, where he worked as head of casualty treaty underwriting and actuarial.
In a career spanning more than 30 years, he has also worked at JRG Re in Bermuda, where he was vice president and chief actuary.
BMS Re Bermuda launched in the fourth quarter of last year, and executive chairman Adam Mullan said the hires “signify our commitment to building an exceptional team”.
“Chris is one of the most experienced and respected brokers in the Bermuda reinsurance and retrocessional market, having held leadership roles on the island for more than 18 years,” he said.
“Mario’s technical and analytical expertise enable us to further develop our casualty and specialty reinsurance offering.”
BMS group CEO Nick Cook said the hires demonstrated a “commitment to building a formidable team”.
“There is huge opportunity in Bermuda for an independent broker of BMS’s ambition,” he said.
“The investment BMS continues to make in talent, innovation and analytics make it the leading independent broker in the market.”