Saints fire head coach Allen after seventh straight NFL defeat
The team said in a statement that special teams coordinator Darren Rizzi would serve as interim coach.
New Orleans won their first two games of the season by margins of 37 and 25 points.
But a 23-22 loss to NFC South division rivals Carolina gave them their first seven-game losing streak since 1999.
"Dennis has been part of our organization for many years. He is highly regarded within the NFL. He has been extremely loyal and professional and most importantly an excellent football coach for us. All of this makes today very tough for me and our organization," Saints owner Gayle Benson said in a statement.
"However, this decision is something that I felt we needed to make at this time."
Allen became the second NFL coach to be fired this season. The New York Jets parted ways with Robert Saleh in October.
Allen, who was New Orleans' defensive coordinator under Sean Payton from 2015-2021, was appointed head coach in 2022.
During his tenure the Saints have gone 18-25 and failed to reach the playoffs.
Several key Saints players have missed time with injuries this season, including quarterback Derek Carr and wide receivers Rashid Shaheed and Chris Olave.
Olave suffered his second concussion of the season in Sunday's defeat.