The 17-year-old centre-back impressed during a trial period with the club’s under-21s, recently playing in the 2-2 draw against Crystal Palace at Selhurst Park.
Head of Football Operations David Burke hopes that Dallison joining is a sign that young players are beginning to realise that Albion is a club where they can progress to the first team.
He told seagulls.co.uk, “We are absolutely delighted that Tom has chosen Brighton as the next stage of his football development.
“The long-term strategy of bringing in players of different ages, in areas we need, is something the recruitment department have been set, and this is another example of a talented player who, for whatever reason, hasn’t been able to find a pathway with one of the Premier League’s top four or five clubs.
“However, he has seen that pathway here at Brighton and he only needs to look at players like Rohan Ince, Solly March, George Barker, Jake Forster-Caskey and Lewis Dunk, to see that players will get the chance to play and train alongside our first team on a regular basis helps progression.
“If Tom hits his performance targets he has a realistic chance of reaching the first team, that isn’t always the case at many other clubs.”
Academy recruitment manager Mark Anderson added, “I have known of Tom for a few years and we monitored him to see how he was getting on at Arsenal.
“When we received the heads-up through our contacts that he may come available, we did a bit of background on him and followed it up, and Arsenal allowed us to take him on trial.
"He played for the Under-18s and scored a header and then played for the Under-21s at Palace and he made a big enough impact on people at the club to encourage us to sign him.”
Under-21 coach Simon Ireland, who played Dallison at Palace, believes the defender will add a new dimension to his side.
“He fits the profile of what we are looking for in a central defender and he is left footed which is certainly a position we are looking for at centre-back.
“He is comfortable on the ball, he looks to step in which is something we encourage, and he has got a good range of passing.
“He also has a good physique which is what you want from a central defender and with that a good work ethic. He also seems keen to learn, which is what you want from any young player.”
Dallison will be available to face Cardiff City next Tuesday in the Professional Development League Cup, where the winners of that tie will host Chelsea in the next round.
Fright Night at the Amex. Buy tickets to watch Albion v Watford on Monday 28th October. Under-16s tickets from just £1 when purchased with a full-paying adult or over-65s ticket. Click here for full details.