Turnbull joins as corporate sales executive in the Kudos catering team. She previously worked in events at Asda.
HIC director Angus Houston said: "Both Tracey and Rebecca have a wide range of experience. They join at a hugely exciting phase in our development, just as our £11m capital investment is underway which will see the opening of two new exhibition halls.
"It is a challenging time for the event industry as the market looks fiercely competitive. We are confident that the investment in our sales and marketing team will pay dividends as we look forward to an exciting future in the business."
HIC made a £180m contribution to the local economy during the 2010/11 financial year, hosting around 150 events and attracting more than 290,000 visitors.
The venue currently comprises eight halls offering 16,500sqm of exhibition space, a modern 2,000-seat auditorium, the Royal Hall with a capacity of 1,000 and the art deco styled Sun Pavilion suitable for up to 200 guests.