It follows a recent financing round that valued Marshmallow at $1.25bn, meaning it has joined the ranks of 'unicorns': new, privately-owned tech companies valued at $1bn or more.
Marshmallow started as a specialist insurance broker that aimed to offer fairer prices for immigrants, expats and 'nomads'. It now delivers car insurance throughout the UK.
MHP + Mischief said it will work alongside the client to "raise the brand’s profile whilst building understanding of the business’ unique proposition and its mission to redefine the sector through a more consumer focussed and transparent approach".
Marshmallow is said to be among the UK’s first black-founded unicorns. It was founded by identical twins Oliver and Alexander Kent-Braham.
Oliver Kent-Braham said: “We have big ambitions at Marshmallow and MHP + Mischief’s stellar track record of working with high-growth businesses like ours made them the ideal fit for us. We look forward to working closely alongside them at this exciting point in our journey.”
Nick Woods, head of financial services at MHP + Mischief, said: "As a high-growth business creating genuine change, Marshmallow fits perfectly into our portfolio. With an impressive management team, a unique proposition and a clear mission and purpose, the business is well placed to transform the industry at a time when changing consumer behaviours demand it.
"We’re delighted to help them tell their story as they continue to challenge the status quo of the sector.”
In March, Marshmallow partnered with ClimatePartner on a programme to cover the carbon offsetting costs for the first 500 miles of any new policy.
Engine MHP + Mischief said it has added 15 new clients in its financial services practice since the start of the year, including open banking platform Plaid, ESG-focused investor Sustainable Funds Group and cryptocurrency infrastructure provider MoonPay. It has also supported fundraising for firms including ecommerce platform Wayflyer and UK fintech group Curve.