Hearnden left HL in January after 15 years, latterly working as a senior analyst, citing a desire to spend time with her family, but has been offered a more flexible schedule at Parmenion.
A well-known media commentator, she will focus on day-to-day fund research but will take a greater interest in managing investment risk, helping Parmenion develop its risk-based solutions.
Parmenion currently has £1.1bn total assets under management, the majority of which is held on the platform.
Hearnden joins the existing investment research team, adding that she was excited to be working with a young business with ambitions to continue its rapid growth.