PRWeek reported that the Taiwanese mobile manufacturer was looking for help to drive sales of its make-or-break phone in May.
Dynamo will work closely with HTC's longstanding agency Nelson Bostock to bolster existing comms efforts for the HTC One, which was launched in the UK in April.
HTC global director of consumer and product PR Julia Herd said that the brief would run initially until September, but added: 'We'll see where it goes.'
Dynamo 'brought some different thinking from the other agencies it was up against and had a good relationship with Nelson Bostock', said Herd.
She also outlined her aim to continue expanding the reach of HTC from a core tech-savvy fanbase to a wider lifestyle audience. 'We've been doing a lot but there's always more to be done,' she said.
Dynamo will work on activity 'across the board', which is set to include specific work on upcoming partnerships that have yet to be unveiled.
Dynamo creative MD Peter Bowles said it is the most significant win to date for the two-year-old agency.