The 48-year-old, from Nairn in the Scottish Highlands, was inspired to take up the challenge following the death of Reece Spark, a close friend of her son’s, in August 2020.
Reece, aged 18, passed away following a battle with his mental health.
Mum-of-three Leanne took up the 365 challenge, which does not permit the use of a wetsuit, after hearing about it on social media.
The NHS auxiliary nurse was joined by supporters and swimmers on Saturday as she completed her final 365th swim.
Leanne posted about her momentous achievement on Sunday, writing: “Good morning all, so this is it #365seaswimchallenge is complete.
“Just want to say a huge thank you to absolutely everybody who turned up yesterday to support me on my final swim-along in and out the water.
“Also a huge thank you to all for the donations for #mikeysline this will make a huge difference.
“I am still overwhelmed from yesterday when a community came together for such a good cause.
“My fellow swimmers who have supported me also throughout the year you know how grateful I am everyday for you guys being in my life.
“Chris Thomas, thank you for setting up this challenge. It definitely was something else but it kept me focused.
“Reece you were in everybody’s heart yesterday, your mum did you proud.”
Social media users left comments hailing Leanne for her incredible accomplishment.
One person said: “That’s amazing, well done, what a star.”
Another wrote: “Well done Leanne you have done Nairn proud!
One social media user said: “Well done, absolutely fabulous.”
While another added: “What an achievement, well done.”
Speaking today, Leanne said: “One of my son’s best friends took his life just before his 19th birthday.
“We have lost a few young people in our community to suicide in the last few years.
“So I decided to do the challenge to raise money for Mikeysline, a local mental health charity.
“I’ve swam in the Moray Firth, I have been in Wales and the Cheswick crossing.
“I had to fit my swims around my work and horse.
“I was in the water and it was 1.4 degrees in the water and it was -2 degrees in the air, there was snow and ice all around me.
“In the summer I wasn’t just going for a dip, I was doing 5km swims, but at the moment I’m lasting about 20 minutes.
“There were a lot of solo swims, but I have an amazing network of friends behind me that joined me.
“In the winter you go to work, it’s dark. Come home from work, it’s dark. Sometimes I was working seven or eight days in a row, but then I remembered why I was doing it.
“I just love it, it’s really hard to describe – it’s the freedom and it gives you such a clear head.”
On finishing the challenge at the weekend, Leanne added: “On Saturday I had my first cry.
“My friend who lost her son was there.
“On Sunday I was like ‘it’s over’.
“But now I’m quite buzzing, I thought I would be down about it, but I’m not.
“I’ve got quite a drive behind me now.”
Leanne has raised over £1,800 so far on GoFundMe.
To donate, please visit: https://www.gofundme.com/f/28oimcnqxc