'ICI has grown incredibly during the past few years, so therefore the need to develop communications to reflect that change is very important,' said Karian.
The role will cover all aspects of the business and employee communications, maintaining relations with the group's divisions, which include both the paints section and flavouring and fragrances arm, Quest.
'There will be work not just on the systems but also the media we use - I will look at how we can develop all media and communications tools, making sure they meet the need of the employees and the business,' added Karian.
Reporting to ICI comms director Penny Studholme, Karian, who will start in two months, will not lead a team directly, but will draw on PR department resources.
He replaces internal comms manager Regina Kilfoyle, who has been promoted to corporate communications manager. Kilfoyle herself replaces Samantha Hunter, who has left the company.
Alongside Karian's former work for the Labour Party, he also worked as a comms executive at WHSmith, handling media relations and internal communications, after which he served as an account director at Edelman PR Worldwide's PR21 consultancy.
ICI, which owns brands such as Dulux paints, has recently made efforts to reduce its £3bn debt. The firm raised £807m in March from a rights issue and it also announced that 1,300 staff are to be axed during the next two years.
Karian's move leaves a void in the top internal comms role at Rolls-Royce, the defence aerospace, marine and energy conglomerate.
He had been at Rolls-Royce for 18 months. Sources at the firm remained tight-lipped as to their plans to replace Karian.
The group's head of corporate media relations, Martin Brodie, said an announcement about internal communications would be made in 'due course'.
News of Karian's departure follows just weeks after Rolls-Royce announced it was to launch the second phase of its group-wide internal comms audit (PRWeek, 26 April).