The agency will advise the committee on comms as it battles critics of China's human-rights record.
The agency's offices in China and the US are working on the account, won after an eight-way pitch. The final shortlist included Weber Shandwick and Burson-Marsteller.
Beijing successfully bid for the Olympics in 2001 with support from WS and Bell Pottinger in Europe. After a year it retained B-M, which worked on projects such as the launch of the 2008 Olympics logo.
At the start of 2005, Beijing tendered for a new retained agency, the account that H&K has now won. The brief does not involve projects such as the torch relay, which is currently out to pitch.
Beijing is one of the most contentious venues chosen to host the Games.
In a recent BBC News report, former Olympic rower Matthew Pinsent visited a sports school in the capital and discovered evidence of child gymnasts being beaten by their coaches.
This Wednesday's Daily Mail showed photographs of lions tearing apart a live ox as Chinese bloodsport spectators looked on.
One PRO told PRWeek: 'This is just the tip of the iceberg; it's typical of the sort of press coverage China can expect to receive.'