The 20-year-old has signed a two-year extension which will see him remain at the Cooper Associates County Ground until at least the end of the 2023 season.
Kasey joined the Somerset Academy in 2018 after spending two years on the Potential Somerset Player Programme and signed his first professional contract in August 2019.
The fast bowler and middle order batsman, who was educated at Millfield school and developed his game at Brislington CC and Bath CC, has progressed through the Somerset CCC Age Group Pathway and England Under 19s, where he featured for his country in the U19 World Cup early last year.
After signing his extension, Kasey said: “It’s an honour to play for the club that I’ve grown up at. This is where I want to play my cricket and I don’t think there’s anywhere better for me to develop.
“It means a huge amount to have been given this opportunity and I can’t wait to go out on the field and impress.
“As a bowler, I’m still developing but to know that I’ve got the backing of everyone at the club is really encouraging.”
Somerset Director of Cricket, Andy Hurry said: “Kasey has all the attributes that you require to be a top-quality cricketer. We have been impressed by the manner in which he adapted to life as a professional player and we are excited by his potential and the opportunity to continue to work with him over the next few years.
“He took the step up in his stride last year and everyone has been impressed by his attitude and his desire to improve every single day.”
Head of the SCCC Talent Pathway, Steve Snell said: “Kasey has huge potential, and it has been superb to see him continue to improve within the professional environment.
“In addition to Kasey’s qualities with the bat, his key attributes as a bowler are that he possesses pace and bounce, and it has been pleasing to see him continue to develop and bowl a threatening line and length more often. He has a number of excellent role models across the club to train with and pick the brains of.
“Securing his future ensures he has more time to continue to develop and start to challenge for a First XI spot, which of course is where he will want to transition to as soon as possible.”