The first 200 customers through the main entrance received M&S golden tickets with vouchers up to the value of £200 to enjoy in store.
First in the queue on Wednesday was Kathryn Brunton, from Lesbury, who turned up two hours before the store opened.
“It was a nice morning so I thought I’d come along and as I was first I started the queue,” she said.
Another early bird was Leanne Davison, from Alnwick, who added: “It’s good quality food and it’s good to treat yourself now and again.”
Robert Twyford, from Longframlington, said: “I’m sure I can speak for most of my friends and family when I say we have been really keen for an M&S to open in Alnwick! It’s been a much needed and exciting addition to the area.
“The size, brightness and accessibility of the store has really impressed me. It makes shopping for the family a really pleasant experience.”
The 40-strong team at the new store were all recruited locally.
Andrea Roberts, store manager at M&S Alnwick, said: “The team has been working so hard to get ready for the opening and it’s been brilliant to see the community turn out to support us today.
“We’re excited to be part of the Alnwick community, and we can’t wait to get to know our local customers.”
The ribbon was cut by Mayor Lynda Wearn who was joined by M&S staff, Colin the Caterpillar and representatives from the store’s charity of the year, HospiceCare North Northumberland.
She said: “It’s nice to have a high-end food retailer in Alnwick. It’s been long-awaited and I am sure it will be popular.
“I hope the local shoppers in M&S don’t forget that we have lots of lovely shops in the town centre and hope they will continue to support them.”
It is the third retail unit to open on the retail park, developed by Northumberland Estates.
Turnbull’s Northumbrian Food Hall opened in December, while Starbucks was first to open in November.