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The 21-year-old, from Meon Valley Golf Club, followed in the footsteps of fellow Hampshire golfer Scott Gregory in 2016 by winning the trophy.
The victory guarantees Ellis will play at Royal Birkdale next month as well as the Masters and US Open next season.
"The magnitude of what I did is starting to sink in," Ellis said.
Ellis came from four holes down with five remaining in the 36-hole final to beat Australia's Dylan Perry at Royal St George's in Kent on Saturday.
Victory was only secured after two play-off holes for the man who became the youngest to win the English Amateur Championship, aged just 16, in 2012.
"I still feel a little numb," he told BBC South Today. "The task was getting a lot tougher to come away with the trophy and I knew I just had to keep myself going.
"It all came out when the winning putt was sunk. It was years of hard work and a lot of disappointment matched with the excitement of holing that putt."
Ellis has just completed his third year on a scholarship at Florida State University, where he hopes the experience will stand him in good stead for an appearance at Augusta next season.
He revealed US Open champion Brooks Koepka was among those to text their congratulations after Saturday's win.
"Justin Rose and Scott Gregory also sent some nice messages," Ellis said. "It's been really nice to receive those and I'm really excited for the opportunities ahead."
The Open begins at Royal Birkdale on 20 July.

You'd expect such a statement from a player who had played for 11 different clubs in three different countries, but how many players have done that at the age of 23?
Meet Jake Jervis, one of Plymouth Argyle's five summer signings, who is preparing for a campaign in League Two having played in Turkey, Scotland and all three tiers of the Football League.
"It's made me a better player to have played in different leagues and different places," he tells BBC Sport as he settles into the final week of pre-season at his new club.
Jervis began his career as a promising youngster at Birmingham City - he once played against Didier Drogba, David Luiz and Frank Lampard as the Championship club held Chelsea to a 1-1 draw at Stamford Bridge in the FA Cup in 2012.
After three years of trying to make the Blues first team, he left St Andrew's in January 2013 for Turkey, where he signed a three-and-a-half-year contract with top-flight side Elazigspor.
But it was a move that did not go according to plan.
Jervis said: "Teams like Fenerbahce and Galatasaray have a crazy atmosphere and it was definitely something that helped me in terms of my football.
"But after three games, having started so well, I broke my foot."
The Turkish club stopped paying Jervis, but when he tried to leave they held on to his registration and he could not join another club until January 2014, a period of six months where he was not able to play the game he loves.
"It was the most difficult thing I've had in my life," he says.
"I was at Sheffield United and I was going to sign there, and I trained with a few other teams as well, but I couldn't get it through because of international clearance due to the old club.
"I was a handful to be around with my girlfriend and my family because I wasn't happy at all not being able to play football."
It was eventually sorted out and Jervis signed a six-month deal at Portsmouth, before moving to Ross County that summer, where he linked up with current Argyle boss Derek Adams for the first time.
"He's 23 and he's only at the start of his career, but he's had a lot of experience," Adams told BBC Sport.
"We're hopeful of progressing him. He did very well for me at my last club and, although I was only there for a short space of time with him, you could see the potential."
Jervis signed a one-year deal at Plymouth in June, so is now the time to try and settle with one club?
"You always look to do that," he said.
"But it's got to be right and you've got to be able to enjoy it. Hopefully we can settle here and go on and do well."
Harry Ellis admits he still "feels numb and in shock" after securing his spot at The Open in July by winning the British Amateur Championship.
[NEXT_CONCEPT]
"The good of football, the bad of football, I've seen all of it."