The 37-year-old, originally from Wrangle, was named High Performance Coach of the Year at an awards bash the Tower Hotel, London on Thursday.
Marshall - who has already been named British Swimming's Swimming Coach of the Year - crowned off a superb year in style after guiding Adam Peaty to become the first man to break 57 seconds in the 100m breaststroke.
“It’s a real privilege to win on a really nice evening and especially to hear some of the stories in the room today," Marshall said upon collecting her award.
"It’s great to celebrate other people’s successes. As a coach, I love seeing people flourish and I’ve always wanted to be that person that can help somebody to realise their dreams.”
Based at Loughborough’s National Centre for Swimming, Marshall – a multiple world, European and Commonwealth swimmer turned coach – has enjoyed a long-time relationship with Peaty, which goes back to when the breaststroke specialist was 12.
He has broken world records and won multiple Olympic, world, Commonwealth and European titles.
In 2019, Marshall coached Peaty to become the first man to swim the 100m breaststroke in under 57 seconds at the World Championships – a title he ultimately won along with two other disciplines.
Marshall was part of the Great Britain coaching team at that event in South Korea and also supports the next generation of coaches through the England Talent Coaching Programmes.