Ms. Cahill, an ally of the D.N.C. chairman, Tom Perez, since he worked with her in the office of Senator Edward M. Kennedy, ran the last Democratic presidential campaign against a Republican incumbent in the White House, when Mr. Kerry challenged President George W. Bush.

Mr. Biden’s campaign manager, Jennifer O’Malley Dillon, praised Ms. Cahill’s appointment to lead the party.

“Mary Beth’s experience running presidential campaigns and managing the kind of complex operation it takes to win a general election will be invaluable, and I am thrilled to have her as a partner in this fight,” Ms. O’Malley Dillon said.

In addition, Greg Schultz, Mr. Biden’s former campaign manager, has been dispatched as a liaison between the campaign and the D.N.C. for the general election. He was replaced by Ms. O’Malley Dillon in March.

Another looming organizational choice for the Biden campaign is whether to contract with a digital services firm called Hawkfish that was created by Mr. Bloomberg ahead of his presidential run. The firm has pitched itself to run much of the Biden campaign’s digital operations, rather than the campaign building out its own internal operation, according to people familiar with the matter.

Hawkfish has quickly become a flash point in the party. Several Democratic digital operatives have warned the Biden campaign publicly and privately against contracting with Hawkfish, arguing that the firm has limited political experience and that its lone big race — for Mr. Bloomberg — did not include any fund-raising or efforts to spend money efficiently. Both are major imperatives for the Biden campaign.

On the other side, the firm is promising access to large amounts of data it has collected and fresh know-how from a Silicon Valley team imported from outside the usual circle of politics.

Whether or not to use Hawkfish is a hot-button decision thrust onto the desk of Ms. O’Malley Dillon, though conversations with the firm predate her taking over the campaign.