The 22-year-old cost the Toffees just £60,000 when they bought him from Sligo Rovers in January 2009 and his progress since then has seen him establish himself in the first-team squad.
That development - and the potential for significantly more - saw Moyes tie the Irishman down to a new five-and-a-half-year contract .
"He deserves it as he's worked really hard since the early days when we brought him in from Ireland," said the Scot.
"Seamus is one of the young boys. He is improving. He came as a right-back and we've used him wide right and he has got his chance to settle in and I feel I can use him in either position whenever needed.
"He's a long way to go to get to Leighton Baines' (who has been a permanent fixture on Everton's left for years) standard at the moment but that's why we've kept him for a long time because we think there's a chance of good improvement in him.
"Hopefully he will continue to improve. You need a good work ethic and Seamus has that and is improving all the time.
"We got him for very little money and it was great business by our scouts to spot him and bring him in."