Brandon Bailey is the new head coach of the Maine Red Claws.

Bailey takes over from Scott Morrison, who was promoted to Boston Celtics assistant coach after leading Maine to three straight Atlantic Division titles in the D-League, which has changed its name to the G-League.

“I’m really excited,” Bailey said Wednesday. “I’ve only been up (to Portland) a few times, not as much as I’d like, but I made it to a couple of games last year and I’m really excited about the atmosphere.”

Bailey, 31, is entering his seventh season with the Celtics, starting as an unpaid intern in 2011 and working his way up from assistant video coordinator to head video coordinator. He’s also done scouting with an emphasis on defense.

“I think he’s going to do a real good job because he’s well-prepared and a big-time student of the game,” said Morrison, who is in San Diego, working out a few potential Celtics free agents. “He hasn’t been a head coach so I can’t speak for his style, but I’ve seen him lead drills in practice and he carries himself well on the floor.”

Among the opposing coaches Bailey will face next season is Josh Longstaff, a 2001 Portland High graduate who recently was named head coach of the Erie BayHawks, a franchise owned by and affiliated with the Atlanta Hawks.

Longstaff, 34, had been an assistant coach with the New York Knicks for the past three seasons. Like Bailey, Longstaff got his start working in the video department, with the Oklahoma City Thunder.

“I spent a lot of time in Boston during the two months I was out of work and met Brandon,” said Longstaff, who also spoke with Brooklyn, San Antonio and Oklahoma City after parting ways with the Knicks this spring. “I went to a Celtics summer league practice and he was running a lot of it. He wasn’t the head coach but he was heavily involved. He had a great presence. I think the people here are going to like him.”

Bailey grew up in Chicago and played for his father at Saint Patrick High. He was a student manager for the women’s basketball team at DePaul University and, after graduation, was hired as a graduate assistant for the men’s team. His only head coaching experience came that summer, for the Illinois Wolves AAU travel team. He was working a summer basketball camp when he met Mike Procopio, the player development director for the Dallas Mavericks, and Procopio helped arrange the unpaid gig with the Celtics.

Bailey said Celtics Coach Brad Stevens and the president of basketball operations, Danny Ainge, surround themselves with young, hungry assistants eager to learn.

“They’ve got a great culture there,” Bailey said. “Brad’s given me unbelievable opportunities to grow and run with the defensive side of the ball.”

Bailey said he doesn’t yet know about the Red Claws’ roster or assistant coaches for the upcoming season. Stevens first mentioned the possibility of the Maine job at the end of the season but the official offer didn’t come until last week.

“I’ve been having conversations with Brad and Danny, and I’ve obviously talked with Scott about his experience and how much he loved it up there,” Bailey said. “I definitely jumped at the chance when they offered it.”

Bailey and his wife, Julie, a nurse, have a 3-year-old daughter and a 6-month-old son.

“He’s going to do a good job,” Morrison said. “No one knows the Celtics stuff better than he does.”

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