A product of the Rangers and Heart of Midlothian youth systems, Leonard will be competing against the likes of Shaun McWilliams, Jack Sowerby, Ben Fox and Peter Abimbola for a central midfield slot at Town.
And the Glasgow-born player says he will be comfortable and fit in wherever he is asked to by his new boss.
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Asked about his strengths, Leonard said: "As a midfielder, I do a little bit of everything.
"I can defend, attack, create and stop attacks.
"I have played in all positions in the midfield three, so I am really looking forward to showing that to the fans and to the management staff who have put their faith in me."
Leonard does have some senior experience, having made two starts for the Brighton first team in the Carabao Cup last season, and he has played a batch of games for the Seagull's Under-21s in the Papa John's Trophy over the past couple of years.
He captained them last season, including in a 2-1 win over the Cobblers at Sixfields in November, and also skippered Brighton's Under-23s in their Premier League 2 campaign, playing in 22 of their 26 league games.
Leonard has also tasted international football, having represented Scotland through the age-groups, and captaining the Under-18s.
He was handed his Under-21 debut by head coach Scott Gemmill last season, and went on to make seven appearances in the Scots' 2023 European qualifying campaign.And he feels that experience has added another string to his bow.
"I played seven or eight games for the Under-21s last year which was really good," he said.
"It was good for me, I enjoyed it, and it was something different to the way we played at Brighton.
"That was a really good experience for me, and one I am grateful for."
As well as playing in the Carabao Cup last season, Leonard also made the match day squad for Premier League matches on 10 occasions, without actually making his debut.
That is still very much an ambition of his, and the Seagulls have high hopes for the player, but the club's pathway development manager Gordon Greer believes the time is right for Leonard to get out on loan.
“This is Marc’s first loan away, so we’re looking forward to seeing how he progresses and develops his game," said the former Scotland central defender.
“We will monitor his development and we wish him well for the campaign.”
Leonard is the second young Scot to join the Cobblers on loan from a Premier League club this season, following in the footsteps of Kieran Bowie from Fulham.