The 21-year-old attacking midfielder will train with his new team-mates this week having had his season-long loan with Boca Juniors cut short at the end of January.
Mac Allister originally joined the club 13 months ago from Argentinos Juniors and since then has gone on to make his senior debut for Argentina as well as helping their under-23s qualify for this summer's Olympic Games tournament in Japan.
He said, “I don’t know if there is a lot of expectation here but, if there is, I am happy about it.
“I’m happy that the Brighton fans expect a lot of me because I have a lot of expectation of the team and of doing well myself.
“Let’s hope that is the case, for the good of Brighton. I thank the club for trusting in me last year when I signed and they are doing it again and I’m excited to get going.”
Mac Allister has kept a close on eye on Albion’s Premier League progress during the last 13 months and believes the style of play introduced by head coach Graham Potter will pay dividends and it’s something he is looking forward to being part of.
“I have seen quite a few Brighton matches and I think the team have improved a lot in terms of trying to play football,” he added. “It’s a different style of football and we haven’t had the results after a good start to the season but the football is better and I’m sure results will improve.
“I’m looking forward to the challenge. I won’t put pressure on myself because I want to enjoy my football here and I’m sure I will.”