Diggs is the star of TV's "Private Practice" and was an original cast member of the Broadway musical "Rent."
During the past few months, Tide -- in partnership with The St. Bernard Project, a grass-roots, non-profit that provides direct support to families -- rebuilt 10 homes in hurricane-ravaged St. Bernard Parish.
After the hurricane, the laundry detergent company also established a mobile laundromat to provide free services to Katrina victims.
Diggs was joined in caroling by New Orleans' Vero Gospel Choir, Grammy Award-winning soul singer Irma Thomas, BET's "Sunday Best" winner Crystal Aikin and St. Bernard Parish families, Tide said.
"I spent time visiting a number of families in New Orleans. They told me that this is the first time in two years that they will be able to enjoy the holidays in their own homes. I feel privileged to have had the opportunity to help Tide support such a worthwhile cause," Diggs said in a statement. "I encourage everyone to join them in doing everything possible to continue to help this city."