Fretwell will oversee the use of data for the company's customer insight services across all of its channels, and will have a data strategy team under him to coordinate data collection and management, campaign planning and return on investment analysis.
He joins from FCBi, where he was worked for the last seven years, and was responsible for data analysis and customer strategy planning for the Sony Consumer Electronics, Motorola, BT and Waitrose accounts. Before joining FCBi he was an associate director at Experian.
His appointment will involve him working closely with Dan Thwaites, the agency's planning director, and he has specific responsibility for the company's Honda UK prospect and customer databases.
Thwaites said: "Neil's experience and clear thinking can really help us continue to develop our offering. He joins us at a time when the agency is increasing its client list and headcount, a validation of our belief in strong planning skills and detailed insight."
Fretwell said: "There's a huge range of experience in the planning teams at Hicklin Slade and I'm excited about the opportunity to push forward our insight and measurement techniques across all our channels."
Hicklin Slade's last head of data, Neil Cook, left the agency in the autumn.
Earlier this month, the agency created an insert and online campaign to complement Honda's "More forwards please" ad push featuring its Asimo robot.