Place, which was launched at the end of 2010 by former LCA directors Ben Ruse and Kate Fisher, has been appointed by HS1, the owner and operator of the UK's first high-speed railway line.
The line runs from London to the British end of the Channel Tunnel.
The brief was held by LCA, where both Fisher and Ruse worked on the account, since 2005. The deal was repitched in March, when LCA declined to participate.
HS1 business services director Richard Martin said: 'London Communications Agency has done a fantastic job for us over the past six years. While LCA declined to repitch, Place demonstrated the ability to continue, and build on, that record in a very competitive process.'
Place will lead comms for the HS1 rail link, St Pancras International Station and the three other international stations along its route - Stratford International, Ebbsfleet International and Ashford International.
The 18-month contract follows a six-agency competitive pitch process. The brief encompasses corporate, consumer and stakeholder work and is understood to be worth a six-figure annual fee.
The appointment comes as high-speed rail travel sits at the centre of UK transport policy. The Government is considering whether to give the green light to a new express line from London to Birmingham.
The agency is expecting to focus on demonstrating the long-term economic benefits of high-speed rail, pulling in people who are not currently customers.
Last November, the Department for Transport and London & Continental Railways sold HS1 to a consortium of Borealis Infrastructure and Ontario Teachers' Pension Plan.
Before working at LCA, Ruse was an associate director at Freud Communications, while Fisher has formerly worked at Fishburn Hedges and as a Whitehall press adviser.