Emanuel made the announcement in a video posted Sunday on his website, ChicagoforRahm.com. He had been careful not to launch his candidacy from Washington and headed to Chicago immediately after his resignation was announced by President Barack Obama on Friday.
In the video, Emanuel said he's embarking on a "Tell It Like It Is" listening tour of Chicago.
"As I prepare to run for mayor, I'm going to spend the next few weeks visiting our neighborhoods - at grocery stores, L stops, bowling alleys, and hot dog stands," Emanuel said.
The two-minute video shows a relaxed Emanuel sitting behind a desk wearing a white shirt that's open at the collar and a dark jacket. Behind him is a photo of his family and several books.
In making the announcement in a YouTube video, Emanuel appears to be following in the online footsteps of Obama, who was successful in galvanizing support among younger voters with a strong Internet presence and near constant contact through text messages, e-mails and Facebook notes.
Emanuel's website offers several options for receiving updates, including e-mail and text, and nearly 12,000 Facebook users had "liked" his page by Sunday afternoon.
Lori Goldberg, an Emanuel spokeswoman, said the online video was an attempt to reach as many people as possible. Emanuel plans to make "a more formal announcement" after the November election.
"By having the website up, it also allows people to communicate with him," Goldberg said.
Bruce Newman, professor of marketing at DePaul University, called the online announcement "a clever move."
"(Emanuel's) ability to communicate via the social media will be critical to his success," Newman said. "The voter in today's world is tuning in to a whole different level of communication."
But other political analysts said the online approach won't work for all voters.
"This is going to be a Generation X campaign with Facebook, Twitter and all that ... but you should never forget the power of friend talking to friend, neighbor talking to neighbor," said Tom Manion, a longtime political operative who directed Chicago Mayor Richard M. Daley's first re-election campaign in 1991.
Indeed, one of the challenges facing Emanuel in a mayoral run is reconnecting with Chicago voters after his time in Washington. Emanuel highlighted his ties to Chicago in the video Sunday, noting his three terms representing a North Side district in Congress before serving as Obama's chief of staff.
"It was a great honor to work for (Obama), but I'm glad to be home," Emanuel said.
Emanuel's website says his family's home is in Chicago's Ravenswood neighborhood. But a tenant recently re-signed a lease for the home, leaving Emanuel to rent a condo closer to downtown, Goldberg said.
She said his three children will stay in Washington to finish the school year.
Daley announced last month he will not seek a seventh term.
Emanuel joins a crowded field of Democrats who have announced they're running for Chicago mayor or hinted at it. Among them are Chicago School Board president and close Daley ally Gery Chico, Chicago City Clerk Miguel del Valle, Cook County Sheriff Tom Dart and State Sen. James Meeks, who's also the pastor of a South Side Chicago church.
Before Emanuel's announcement Sunday, Chico called on him to release details about his dealings with former Illinois Gov. Rod Blagojevich's administration in regard to the U.S. Senate seat once held by Obama.
Blagojevich will be retried next year on federal charges that he schemed to sell the seat after his first trial ended in a mistrial. Emanuel was not called to testify and hasn't been charged with any wrongdoing.
Del Valle said in a statement before Emanuel's announcement that he welcomes "all candidates to the race and look forward to a spirited campaign."
"This is the first time in 67 years that there is an open seat, and a crowded field will ignite interest and give voters choice," del Valle said.