Casement will take up the new role of sales director after joining as head of sports and events from Zibrant in 2009.
Pat McDonagh will take on the role of CEO from his previous position as head of business travel, with Mark Nevin appointed as CFO and Sue Chapman appointed as commercial director.
On his new position, Casement said: "This is both a continuation of the senior management team and confirmation of the backing from the new owners.
"It is also an expansion of my role where I will have responsibility for all the sales department, including venue-find, the events business, the sports business and business travel.
"Already this year we have launched a number of new products and with the backing of Al Tayyar Travel we will be a launching several more before the end of the year so that we are in prime position to become one of the leading international travel management companies."
Last month, Thomas Cook announced the sale of Co-operative Travel Management to Mawasem Travel and Tourism, the UK subsidiary of the Al Tayyar Group, a Middle Eastern-owned international travel group for a reported £13.5m.