Big will be responsible for media relations and managing the company’s social media channels.
The account was previously held by Birmingham-based digital & PR consultancy Haslimann Taylor.
The account will be headed by Big’s PR partner Bron Eames, who said: "This is a very exciting brief and we look forward to implementing a plan that ensures the profile of Arqadia is kept consistent among the media and customers alike."
Arqadia’s marketing manager Pauline Hutchinson said: "We were impressed with the team at Big who presented a well thought out plan, backed up with thorough research and insights. We are looking forward to building a successful relationship with Big and are excited to see their plans put into place to help maintain our reputation as market leader in the industry."