From being a mascot during Arsenal's Champions League campaign in 2007, she is now a key member of the Arsenal Women team, has played alongside her sporting idols and will now lead England into the inaugural Arnold Clark Cup as captain, at the age of 24.
Williamson is a lifelong Gooner who chose the red side of north London having grown up in a 'split household' - her mother and father supporting rival clubs Arsenal and Tottenham, respectively.
Sport has always been a constant in her life. She almost considered a career as an Olympic athlete and training in track and field after watching Greg Rutherford at the 2012 Summer Olympics in London.
Williamson could have followed the footsteps of fellow Milton Keynes-born star Rutherford, and while she ultimately stuck with her first love, football, she eventually fulfilled another dream by becoming an Olympian with the Great Britain team that reached the quarter-finals of the 2020 Games in Tokyo, Japan.
Speaking to Her Football Hub, she said: "For me, growing up, this [the Olympics] was always something that felt like it was slightly further away, and made it give me all the more reason to want to achieve it.
"So, like I say, it's so surreal to be here [in Tokyo] now. I always had a glimmer of hope. I was always considering what other sport I could do, to get myself to be in a position to be an Olympian, and then settled on football. To actually be here is pretty cool.
"Actually, I was always a good runner - athletics, cross country. I don't think I've ever been a marathon runner. When I was younger, that was always an option for me, in terms of competing locally.
"But I just remember saying - I think my mum actually told me - I said to her 'what can I change to make sure I can be an Olympian?' Because football seemed a little bit unattainable, but I probably wasn't good enough to do anything else, to be honest.
"To be able to do something that you're so in love with, at such a high level, and then being this very sort of sentimental person that I am, to put all the pieces together in such a way… the only thing that could make this any better would be if it was in London, and that I was nine years older."
Williamson started her career on the international stage in 2010, going on to captain England during the 2014 UEFA Women's Under-17 Championship.
In 2015 the Arsenal ace - who began her career as a midfielder but now plays in central defence - grabbed the headlines in a controversial game, as she showed her class and ice cold nerve which proved Williamson was a cut above the rest.
The youngster saw her penalty disallowed during England's qualifying match against Norway in the 2015 UEFA Under-19 Championship, with that decision later overturned and the game replayed five days later.
The match restarted in order to complete the final two minutes with the Three Lions trailing 2-1, and Williamson held her nerve to convert the spot kick which booked England's place in the European Championship finals.
It was a sign of things to come for the versatile young star, who went on to make her senior England debut in 2017 under former boss Phil Neville.
By the time the 2019 Women's World Cup came around, Williamson was already a WSL champion, two-time FA Cup winner and two-time League Cup winner, and yet she struggled for regular minutes for her country.
It's something Neville later admitted he 'regretted', following a host of calls from fans wanting Williamson to feature.
"She's competing in an area where we've got some unbelievable players, Neville said at the time.
"I thought she was frustrated at the World Cup and it was a difficult time for us both because we thought the same thing.
"When I left the World Cup I thought long and hard about it - about how we can get this girl in our team. There comes a point in a young player's development where you physically can't leave them out."
Williamson's future looks bright with new England boss Sarina Wiegman at the helm, who has acknowledged her 'calmness' as the key factor to giving her the captaincy.
With Steph Houghton injured and out of the Arnold Clark Cup, which the Lionesses get underway against Canada on Thursday, Williamson was the natural choice for the armband.
"Leah has always had that ability to play in midfield," said teammate Millie Bright about the versatile ace.
"She leads by example and what you see is what you get. She is a very mature individual, both on and off the pitch. She is very calm in the way she leads.
"It's been a delight to see her lead the team out and it's been a big moment for her. I'm really proud as a teammate. She is really effective in that [midfield] role. It's something different and it's an option."
Williamson has fulfilled a dream to make over 100 appearances for Arsenal, lifting silverware galore and playing alongside her sporting idols who became her teammates, including Kelly Smith, Alex Scott, Rachel Yankey and Emma Burn.
It's certainly been quite a journey since her first walk onto the Emirates Stadium pitch, hand in hand with Theo Walcott as one of the Gunners' young mascots.
The next time she'll make the same walk, Williamson will be doing it with the England captain's armband.
England get their Arnold Clark Cup campaign underway against Canada on Thursday, February 17 - Kick-Off: 19:30.
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