Allain joins from Talker Tailor Trouble Maker, where she was creative lead and worked on accounts including Deliveroo, Poundland and Mastercard.
She also played an integral part in client wins such as Vice’s Change Incorporated platform and Deezer.
"If the past four years taught me anything, it’s to sprinkle some fabulousness even in the most adverse times," she said.
"My first week hasn’t been the traditional way of starting a role but, now more than ever, I’m ready."
Allain will be part of the growing creative team at MSL, helping to expand current clients and work on recent pitch wins.
MSL UK group creative director Michael Dowell said: “What a time to join a new agency.
"The industry has just experienced a huge shift, overnight, and we need culturally relevant creatives more than ever to help our clients navigate a rapidly changing landscape."