Incumbent agency Manifest, which had held the account since March 2016, said last month it had mutually agreed to end its relationship with Innis & Gunn "to avoid a conflict of interest" with its new client BrewDog.
One Green Bean's remit includes communications strategy, integrated campaigns, press office duties and influencer activity to support the craft brewer in the UK. The agency began work this month.
One Green Bean MD Matt Buchanan, who is leading the account, said: "We're big fans of Innis & Gunn and their unique story. They have always innovated and experimented, so the brief presents a great creative opportunity for us and we're looking forward to producing impactful work together."
The agency also announced in May that it had appointed two former Edelman staffers - Cath Jeffries and Chris Warr.