The Watergate HotelCredit: by mastermaq on Flickr. Some rights reserved
His article is part of the Post's special coverage around the anniversary of the political scandal, which will also include essays by investigative journalists Bob Woodward and Carl Bernstein.
The Washington Post will also be publishing an eBook of "The Original Watergate Stories", which will be available from Amazon.
In his opinion piece published on Thursday, reflecting on 40 years since the political scandal, Leonard Downie Jr speaks of a need to make sure such journalism "survives and flourishes in the digital cacophony".
Downie Jr, who was executive editor of the newspaper from 1991 to 2008, highlights in his piece that "we continue to live in perilous times, making investigative journalism as essential to our democracy as the Watergate stories were".
"The impact of digital media and dramatic shifts in audience and advertising revenue have undermined the financial model that subsidised so much investigative reporting during the economic golden age of newspapers, the last third of the 20th century."
As a result he adds that while the Watergate anniversary "will surely elicit where-are-they-now stories", it is vital the occasion is also used to amplify "widespread recognition of the importance of accountability journalism in our democracy".
The article comes days before Washington Post Live is due to hold a forum to celebrate the 40th anniversary on Monday 11 June.
The event, to be held at the Watergate Office building, will bring together "the major players", including Woodward and Bernstein.
According to the event page online "video highlights will be posted following the event on washingtonpostlive.com".
In a press release editor of the Washington Post Marcus Brauchli said: "The Washington Post has a unique place in history because of its role in Watergate, and we couldn't think of a better way to reflecton its legacy than with the key players who started it all".
Two days later, on Wednesday (13 June), the Newseum in Washington DC is hosting "A Conversation with Bob Woodward on the 40th Anniversary of Watergate".