He said Scotland had become a "healthier, cleaner, more just and more confident" place in the 15 years since the Scottish Parliament was established.
Describing devolution as "home rule inside the UK" he insisted it remained the "best and most positive system" for the country.
Lord McConnell, who left office following the SNP's election victory in 2007, will make his first significant intervention in the referendum campaign with a speech for Better Together.
It will mark the 15th anniversary of the state opening of the Parliament by the Queen in 1999.
He also speaks out in a column in today's Herald jointly authored with former Deputy First Minister Jim Wallace, now Lord Wallace.
The pair, who headed the Labour-LibDems' administration together from 2001 to 2005, will appear alongside each other at an event at the Hub venue in Edinburgh.
In his first speech for the No campaign, Lord McConnell will draw on the 15-year history of the Parliament to argue devolution has worked for Scots and is continuing to evolve.
He will cite the smoking ban, land reform and the introduction of free personal care for the elderly as examples of Holyrood legislation that has changed the country profoundly.
Lord McConnell will also hail the abolition of student tuition fees, which were replaced with a graduate tax under the Labour-LibDems' administration, and the present SNP Government's move to allow gay marriage as landmarks over the past decade-and-a-half.
He will say: "The facts prove the success of devolution. We still face huge challenges, but Scotland is a better place after 15 years of devolution.
"We are healthier, cleaner, more just, more confident, economically stronger and better connected. Home rule inside the UK has had good days and bad days, but it works and it will continue to grow and develop.
He will add: "Home rule for Scotland within the UK is the best and most positive system for the people who live and work here.
"Devolution gives us the autonomy to decide our laws.
"Our Scottish Parliament has strong powers to make our own decisions and change lives.
"But we voluntarily share our sovereignty with those who live in England, Wales and Northern Ireland in the areas where it is best to work together."
Writing in today's Agenda column, Lord McConnell and Lord Wallace, now the Advocate General for Scotland, argue that devolution will continue to develop.
Since it was created, Holyrood has gained powers to develop railways and renewable energy and, from next year, responsibilities for levying a range of taxes.
The three main pro-UK parties have all promised to hand Holyrood further powers in the event of a No vote.
The Scottish National Party has argued that what it has described as the "gains of devolution" would be put at risk by a No vote in September.
The party has also cast doubt on promises of further devolution.
But Lord McConnell and Lord Wallace write: "Have the last 15 years been flawless?
"No, but as the slogan says, we're Better Together, not Perfect Together - and that is why we believe those who would break Scotland apart from the rest of the UK are offering a false choice.
"The devolution process was never meant to be set in aspic and it never will be. From the very outset, the settlement has shown itself to be flexible and dynamic."