Dennis Gaskell had been cooking all Sunday morning in the cramped basement just off Downtown Crossing. Now, as the lunchtime crowd arrived, he was beaming with pride as hundreds of the city’s homeless made their way down the narrow stairwell to the kitchen of the Boston Rescue Mission.

“We do this every day, but this day is extra special,’’ said Gaskell who manages the kitchen for the mission where he arrived 18 years ago, homeless and battling alcoholism. “This time of year, these people need something heartwarming.’’

He was referring to the annual Day of Thanks celebration, where the shelter serves a full Thanksgiving dinner — heaping plates of turkey with all the trimmings — to some of the city’s neediest.

Mayor Martin J. Walsh, who was working the line serving turkey, said that the event was both humbling and illuminating for him.

“You just see the need, see these families struggling,’’ Walsh said as he piled a giant turkey leg on a plate. “For all the good things going on in our city, the incredible growth, the need is very real. Things like this make me thankful for what I have, but serve as a reminder of how much we have to do.’’

On the other side of the room, a man named Darin Johnson was digging into his meal. Last fall, the 51-year-old had walked in the door in a bad way, struggling with substance abuse and homelessness.

Now he lives in the shelter, works at the front desk, and is working toward a certificate in substance abuse counseling at UMass Boston.

“Sometimes life just throws a curve at you, and you need a place to help you slow down and gather your faculties,’’ he said.

As Johnson ate, Gaskell, the kitchen manager, ran around the room checking on everyone. When the meal was done, he would help replace the tables with 30 temporary green cots. It was cold out, he said. They were expecting a lot of visitors for the night.

But there was still much to do before that, many more people to feed, and when his phone rang, he assured an anxious person on the other end that he would have turkey for them whenever they got there.

“You ask for Dennis,’’ he shouted into the phone, “and I’ll make sure you have a Thanksgiving.’’

Billy Baker can be reached at billybaker@globe.com. Follow him on Twitter @billy_baker.