Ayers, 62, retiring after 40 years in the department - his 40th anniversary was Tuesday - said he was ready for a Caribbean vacation. He made his intentions known some time ago, giving the administration the opportunity to look for a successor.
"We didn't need a national search because we have some of the best talent anywhere in the firefighter service," Nutter said.
A native of Philadelphia, Ayers was president of Club Valiants Inc., a black firefighters' organization, in the early 1990s. In 2004, he became the second African American to serve as Philadelphia fire commissioner.
Nutter said Philadelphia was safer, stronger, and "better because of his service," citing Ayers' focus on fire prevention.
The rate of civilian fire deaths fell during Ayers' tenure, Nutter said. Last year, 24 people died in house fires, down from more than 60 in the mid-2000s. The decline is similar to nationwide trends.
The fire commissioner's post pays about $150,000 a year. Under the city's deferred-retirement program, known as DROP, Ayers is projected to collect $550,671.
Sawyer, 54, is a Philadelphia native who joined the department in 1985 and has made his way up the ranks.
The soft-spoken Sawyer, a married father of four, joked on Wednesday that he was a "functional introvert."
At 17, he joined the Air Force, and at 25, the Fire Department. He has an associate's degree in fire science from Philadelphia Community College and a bachelor's in public safety administration from Holy Family University. He is pursuing a master's degree in homeland security at St. Joseph's University.
He said he wants to make Philadelphia the nation's safest city. Nutter said Sawyer has 30 days to develop his strategic plan.
Sawyer is also part of a new generation of firefighters moving into leadership roles. "Derrick and I are both part of that generation," Joe Schulle, president of Local 22 of the Philadelphia Fire Fighters' Union, said after the announcement. "Hopefully, we'll start working together . . . rather than being so adversarial."
In other promotions Nutter announced, Jesse Wilson will replace Sawyer as deputy commissioner for operations; Yolanda Stallings will become executive chief for performance and strategic planning; and Diane Schweitzer will be deputy commissioner for administration, making her the first female deputy commissioner in the department.
Peter Crespo was promoted to executive chief, making him the first Latino in such a post. The moves are effective July 1.