Newsplan 2000, supported by a 5m Lottery donation, has scanned more than 12m pages of newsprint from 1,350 different newspaper titles onto 30,500 rolls of microfilm which will last for up to 500 years.
The project team is now distributing microfilm reading equipment to local libraries, where the archives will be freely available for the public to consult.
Tim Bowdler, Johnston Press chief executive, said: "But for Newsplan 2000 and the efforts of all those involved, a vital part of our local history and heritage could have been in jeopardy or lost altogether."
Supporters of the project included Trinity Mirror, Guardian Media Group and The Newspaper Society.
Five-year plan to archive local news complete
A five-year, 7.3m project to scan all local British newspapers produced between 1700 and 1950 onto almost indestructible microfilm has been completed.
