Grindal, who started at Red Door last week, joined Munro & Forster in 2009 and was part of its digital strategy team. She led the high-profile organ donation campaign for NHS Blood & Transplant.
Previously, she worked as head of media and communications at mental health charity Mind.
Managing director Catherine Devaney said the appointment was part of an expansion of the senior management team.
She said: ‘As we move from broadcasting our messages to driving greater engagement and dialogue, developing and promoting share-ready and share-worthy content that lives off- or online is key for successful PR programmes. Finding and nurturing individuals with proven digital and content marketing skills is therefore critical for us.’