Hirst was most recently a partner at City Savvy advising asset management groups on reputation management, international media relations and corporate communications.
She previously founded and was managing director of Par Excellence, where she worked for more than a decade serving the alternative asset management sector.
Earlier in her career, she was a board director at Ludgate Communications, before moving in-house as group director of communications at United Pan-European Communications, then Europe’s largest cable operator.
"Henrietta is one of the best known and most respected senior communicators advising alternative asset management firms, from hedge funds and private equity to sector service specialists such as fintech," Hydra’s managing partner Stephen Benzikie said.
"We are delighted that she has chosen to join Hydra as we continue to build our client list and service offering supporting asset managers and broader financial sector firms."
Hirst added: "I believe that Hydra’s senior-only model for both strategy and execution is a compelling offer. Clients increasingly want specialist insight and added value to complement their own resources.
"I look forward to working with my fellow Hydra partners to develop broad programmes that make a real difference to financial services businesses and beyond."
Hydra offers board-level advice and senior-only execution across all key areas of corporate communications, focusing on supporting CEOs and communications directors.
Its services include corporate, financial, IR, brand strategy, employee engagement and change communications, litigation support and the full range of digital communications.
Hydra’s financial services clients have included UBS, Close Brothers, Invest Europe, Riverside Europe, Duke Street, Endless, Baring Private Equity, Mellon Trust and KAS Bank.