Mellor, a former head of sales at Capital Radio Group, will oversee all trading from First Radio Sales' London offices and will report directly to Neil Webster, managing director.
He was made director of agency sales under Sara Haynes last year, but has been working under a temporary contract at FRS for the last few months. He has 17 years' experience in the industry, including stints at GCap and Piccadilly Radio.
Webster said: "Tony has worked with us for the past few months. He is well respected and has a fantastic relationship with key trading partners.
"FRS continues to thrive despite a challenging advertising market. I am certain Tony's appointment will help to continue this performance."
Mellor described local radio's connection with listeners as "hugely powerful", and said: "I've grown up with the medium and it's a real privilege for me to be doing what I love."