The building was left empty after energy broker Utility Alliance went into administration last February with the loss of more than 200 jobs.
But it is now at full occupancy.
As well as Orangebox occupying the top two floors, they have also welcomed three new business tenants into the building.
Orangebox chief executive Simon Corbett, who also co-owns Tranquility House, said: “We’ve got a lot of relationships in the town and through social media and a bit of advertising we’ve filled the spaces quite quickly.
"I could have filled it twice over to be honest. We’ve got people on the waiting list.
"It has gone really well. I think we have got the best building in the town with the best views.”
Orangebox, which has spent around £250,000 on refurbishing the building, specialises in delivering training services such as first aid to commercial clients and since 2018 has helped hundreds of people find work through its government-funded pre-employment training courses.
Among the big employers it works closely with are Amazon and Tesco.
Despite the pandemic, staff doubled, prompting the firm to look for bigger premises and to relocate from the town’s Queens Meadow Business Park.
After moving into Tranquility House in July, it has been joined by IT company Eden Digital, Bella Marie Beauty Academy, and business energy suppliers Combined Utilities.
Hayley Honnor, of Bella Marie Beauty Academy, which also has sites in Seaham and Sunderland, said: “We opened our doors last September to be able to offer more opportunities to people within the North East.
"A lot of people in Hartlepool can’t travel to Seaham or Sunderland so we wanted to be more accessible.
"It’s a lovely building and is like a big community.”
Combined Utilities Managing Director Paul Anderson added: “We jumped at the chance because of where the building is located and we wanted to grow and make the business more professional.
Law firm Smith and Graham Solicitors are also set to move in later this month in addition to their Church Square offices.
Simon added: “We’re extremely proud of our journey.”