Colchester United had no record of the 1937 meeting until the notes were found in a box of memorabilia dropped off at the club.
The "one of a kind" document records the appointment of the team's first manager and players, as well as a decision about kit colours.
Club spokesman Matt Hudson said the discovery was "hugely important".
"This will help us fill the gaps and tell the story of how the club came about, the foundations of what we are now," he said.
"Without this book, and the decisions made by people who wrote this book, we wouldn't be where we are today."
Mr Hudson said the identity of the book's previous owner was unclear, but he was thought to be a relative of Hal Mason, who wrote a book about the club's history.
When it was officially formed, Colchester United replaced Colchester Town Football Club, which had been running since 1873.
The new club took over the ground at Layer Road, where the side played until 2008 when it relocated to Colchester Community Stadium.
"I think over the last couple of years we've tried to put a bit of Layer Road history back into the new stadium, and the minutes book is another piece of that - potentially the centrepiece," Mr Hudson said.
A typed transcript of the minutes has been prepared so the original item can go on display at a later date.
Mr Hudson said the club was considering holding an "archive day" to showcase the notes and encourage fans to bring in more photos and other memorabilia.
Long-lost minutes of a meeting in which a football club became a professional side have been unearthed.