Kinnear was keen for the 54-year-old, who has instead taken up a role as assistant manager at Championship side Millwall, to work as his right-hand man behind the scenes at St James' Park.
The duo previously worked together at Wimbledon (with the former striker playing under Kinnear), Luton and Nottingham Forest, but Harford has decided against re-joining the Irishman at Newcastle.
Harford spent one season at Newcastle as a player in the early 1980s and has expressed his pride at being approached for a role at the club.
"After meeting with Mike Ashley and Joe Kinnear, I made the hard decision that it is not the right time for me to take up this role," he told Sky Sports News.
"It was an honour to be asked to work at a fantastic club and I have the utmost respect for the Newcastle United and its fans.
"I am currently enjoying a role helping out at Millwall, but would like to thank Mike Ashley and Joe Kinnear for the opportunity."
