The brief, which carries a six-figure annual retainer, has been created to hammer home to the City and business media the company's move from brewing to a broader leisure portfolio of businesses.
Over the past two years Whitbread has sold off its brewing, pub and off-licence businesses to concentrate on hotel, restaurant and fitness centre brands.
Group PR manager Jeremy Probert said: 'We have repositioned the company and it's important this message is actively sent out to specialist media and the City. When people think leisure I want them to think of Whitbread.
Too often we are referred to as a brewing firm.'
Tulchan is now preparing a communications strategy outlining how best to publicise the company's leisure sector role.
Tulchan's team is led by founder Andrew Grant, who reports to Whitbread corporate affairs director David Reed.
Grant said it was important to promote the 'investment case', adding: 'We are looking to come back with our suggestions within weeks when I believe it will go to the board.'
The agency takes over from The Maitland Consultancy, which had a narrower remit, primarily to assist in what Probert calls 'reactive work'.
Tulchan won the account following a three-way pitch in late May. Also competing were Maitland and Brunswick. It is understood that Brunswick chairman Alan Parker took part in the pitch.
The agency is also tasked with media support on potentially lucrative takeover bids.
Whitbread brands include the Marriot and Travel Inn hotels, David Lloyd Leisure and the cafe and restaurant chains Costa and Brewers Fayre.
The restaurant portfolio was slimmed down earlier this year with the sale of its Cafe Rouge and Bella Pasta chains to Tragus Holdings.