The London-based firm said Losey (pictured) will spearhead transition from a consumer-focused comms agency to a "truly hybridised communications consultancy able to solve brands' problems in completeness".
She will also take responsibility for performance, talent management and day-to-day operations.
Unity's recent rebrand included a new brand identity, website and positioning that "focused on building a hybrid consultancy model rooted in purpose-led stakeholder engagement".
The company said Unity has grown fee income 30 per cent and more than doubled pre-tax profit since completing a share buy-back in 2018.
This followed the departure of co-founder Nik Govier and saw fellow co-founder and current CEO Gerry Hopkinson take 100 per cent ownership.
Since then, the agency – which has a headcount of 28 – has added new services including brand consulting, content marketing, employee engagement, CSR, public affairs and issues and crisis management.
Losey, former head of planning and strategy at Grayling, joined Unity in May 2018 to lead the strategic consulting practice. Unity said the practice now represents more than 60 per cent of fee income, working with clients including Lloyds, ADT and AXA PPP healthcare. Unity's total turnover for the most recent financial year is £3.1m.
Unity, founded by Hopkinson and Govier in 2005, has historically been best known for its creative consumer campaigns.
Highlights have included the PRWeek Award-winning Follow the Fairies, Marks & Spencer's 2014 Christmas offering that was recently listed among PRWeek's 10 best PR campaigns of the decade.
Hopkinson said: "After the share buy-back, I felt it was sensible to take some time to restructure financially, and reflect on the direction of the business, and the marketplace. It became clear to me that old school approaches were in serious trouble and communications as a stand-alone offering was inadequate.
"Instead, clients require true consultants who can give them a fresh perspective and guide them through these uncertain times, but also creative practitioners who can execute as well as advise. This was the inspiration for our hybrid consulting model and one that we intend to build on in the future through investment, expansion and new product and service creation.
'We see eye-to-eye'
Hopkinson said that since Losey joined, the agency's pitch rate "has been near 100 per cent and the quality of our work has improved dramatically".
"She is exceptionally talented and brings a complimentary but distinct skillset to the table. More importantly, we see eye-to-eye on vision, culture and ambition," he added.
"Together, we are looking forward to taking Unity to new heights by helping clients grow sustainable share-holder value through purpose. Whilst I’m very proud of where Unity has come from, I’m even prouder of where it’s going."
Losey said: "My career has been a pursuit of the highest level of strategic thinking married with faultless execution and an obsessive interest in audiences and I feel at Unity we can truly achieve the goal that is building excellence in thinking and doing whilst guaranteeing cohesion across all.
"The world has changed, we live in an era where brands can’t just say one thing and do another, they need to live and breathe an authentic, purpose-driven narrative, first time, every time."
Losey joins the Unity board alongside Hopkinson and recently appointed finance director Madelaine Davis.