Jamie Dimon's finally getting his shot to run a big New York bank.

JPMorgan Chase ( JPM) said Wednesday that Dimon, its president, would take the reins as CEO Dec. 31 from William Harrison. Dimon's ascent had been telegraphed but JPMorgan said it accelerated the transition in recognition of the "good progress made on successfully integrating the JPMorgan Chase and Bank One merger."

"With many of our merger milestones completed and financial performance improving significantly, I recommended to the Board that we accelerate the transition," said Harrison, who will remain chairman. "I'm looking forward to doing whatever I can to support Jamie and the senior leadership team as we realize the potential of this outstanding company."

Dimon was once seen as heir apparent to Sandy Weill at Citigroup ( C), but he left in 1998 and later ended up leading Chicago's Bank One. Bank One's merger last year with JPMorgan Chase led to a plan in which Dimon would take over for Harrison at a set time.

The news came as JPMorgan posted a third-quarter profit in line with Wall Street's expectations. The bank made $2.53 billion, or 71 cents a share, up from the year-ago $1.42 billion, or 39 cents a share. Operating earnings rose 23% from a year ago to $2.7 billion, or 75 cents a share, beating the Thomson First Call analyst consensus estimate by 3 cents.

"Results for the quarter were strong across most of our businesses. Trading revenue improved significantly, and investment banking fees remained strong," Harrison said. "In addition to completing the conversion of our credit card portfolio to a new state-of-the-art processing system, we also successfully executed our massive Texas conversion, which entailed uniting the Chase and Bank One franchises in Texas with common systems and branding. These accomplishments set the stage for the New York tri-state conversion. We remain intensely focused on harvesting further efficiencies from our merger, while strategically investing for growth and building a best-in-class franchise," Dimon said.

The provision for credit losses was $2.1 billion, up $348 million from the prior year. The increase was due to a $400 million special provision related to Hurricane Katrina. Excluding the impact of the special provision, wholesale provision for credit losses was a benefit of $149 million for the quarter, compared with a benefit of $137 million in the prior year, reflecting continued strength in credit quality.

JPMorgan was flat at $33.77 early Wednesday.