Kaela Thurston, 34, underwent two operations, seven months of intense treatment and had to learn how to walk again after the disease had a devastating affect on her motor skills.
But the fitness fanatic, who has previously played tag rugby and ran half-marathons, has got her running shoes on again and landed a place in October's 26.2-mile event.
She said: "It's been on my bucket list for a while and so I just thought, 'why not?'
"I've been absolutely loving the training and I can't wait to race."
Marketing manager Kaela was six months pregnant with her second son Lachlan when she received the heartbreaking news she had a brain tumour in June last year.
Kaela struggled for around six months before her diagnosis with headaches, fatigue and neck strain and wrongly believed she was experiencing symptoms of pregnancy.
However an MRI scan revealed a brain tumour and she was rushed to theatre for emergency surgery to have it removed.
She then spent an agonising two weeks in hospital, where she relied on "wonderful" NHS staff to do "everything" - including walking.
Kaela said: "I was overwhelmed by the skills of my surgeon and sincere care I received. I couldn’t walk and relied on the wonderful NHS staff to do everything."
The situation went from bad to worse two weeks later when doctors told Kaela the growth had developed into cancer, meaning she would need radiotherapy and chemo.
But before beginning treatment, she faced the terrifying prospect of giving birth while battling the potentially fatal disease.
On August 12 last year, Kaela bravely gave birth to her 5lb 9oz baby boy via C-section, who was fit and well but pent a night in intensive care for monitoring just in case.
She said the moment was "bittersweet" as she took joy in Lachlan's arrival but her ongoing cancer battle was always in the back of her mind.
Kaela added: "I was going through the happiest and saddest moments of my life at the same time.
"Lachlan was perfection. I now had two boys under two. The love I felt for them gave me the greatest distraction from my diagnosis."
Tragically, Kaela's tumour had grown back during her pregnancy, so she needed further surgery to have it removed in August last year.
She added: "Leaving my two-week-old baby while I recovered in hospital was heartbreaking, but he was with his daddy, he was safe, he was happy."
"Being away from my baby and toddler every day, continued to be agonising, it was the hardest thing I’ve ever done and was so happy when it was over."
Six weeks later, she underwent a brutal course of 30 sessions of radiotherapy, followed by chemo, before finally finishing treatment in April this year.
Since then, the mum-of-two has enjoyed spending time at home in Queensbury, Bradford, with her little ones and partner, and has started training to compete in October's London Marathon.
Kaela has also joined her local Queensbury Running Club, who she described as “supportive” and “motivational” on her journey.
She said: "After everything I've been through it feels amazing to be out there on my own keeping fit.
"I'm so happy to be where I am now. I'm loving spending time with Lachlan and Harrison and the running has been a great outlet for me too.
"I can't wait to run the London Marathon, it's been on my bucket list for a while."
In January this year, Kaela began chemo but fortunately only had to do two rounds before stopping.
In April her treatment finally ended, although the cancer Kaela has is incurable, meaning she will never be given the all-clear.
However, recent tests have shown the growth has not increased in size, which Kaela says is "good news" and the best she can hope for.
Kaela is raising money for the Brain Tumour Charity. Visit: https://uk.virginmoneygiving.com/fundraiser-display/showROFundraiserPage?userUrl=KaelaThurston&pageUrl=1 to donate.