Henfrey decided to leave his position last month after a year-and-a-half in the role, and will formally step down on March 29.
Marcus Blackmore is the son of company founder Maurice Blackmore. He first joined the business when he was just 18 years old, and has served on its board since 1973, including as executive chairman until 2017.
The company said today: "Marcus has a proven commitment to Blackmores and is a giant of the natural health industry. In this interim role, he will lead the work to streamline the company, to achieve ongoing success for our business, our people and our shareholders.
"Marcus holds an Honorary Doctorate from Southern Cross University for distinguished leadership in complementary medicines in Australia and an Honorary Doctorate of Letters from Western Sydney University for his distinguished services to business, charity and the broader community. He was awarded a Member of the General Division of the Order of Australia in 1998."
Blackmore will remain in the acting CEO role while the Board undertakes the search for a new Chief Executive Officer.
The firm added: "The Board takes this opportunity to once again thank Richard for his service and leadership of the Group over the last 18 months and for his strong commitment to Blackmores, the industry and our stakeholders over his decade long tenure."
Blackmores half-year numbers caused market jitters after sales in China fell 11% to US$46.3m (A$65m).
This was despite the company achieving overall 'record revenue' of US$227.2m (A$319m) — up 11% from the same period in 2017 — and net profit after tax of US$24.2m (A$34m), which was "in line with the prior corresponding period".