Bradley's family announced the six-year-old Sunderland fan had died on Friday and celebrities across the world of sport have expressed their sadness.
Sunderland goalkeeper Vito Mannone, who joined team-mate Jermain Defoe at Bradley's sixth birthday party in May, said his heart was broken.
The Italian told his Instagram followers: " I wished this day would never come. My heart is broken and I have no words but i want to remember your incredible smile and I am honoured that I met you and had the chance to spend fantastic moments with you little Bradley and your family.
"It is like losing one of my family and from today I will have someone more to make proud anytime I step onto a football pitch.
"I am sure god have a place for you up there where you can spend amazing moments playing football without suffering anymore.
"My prayers go to all the family and people connected to @bradleysfight. I will miss you forever kiddo. RIP."
Former England captain and Match of the Day pundit Alan Shearer tweeted: "So sorry that little @Bradleysfight has passed away. An inspirational life cut way too short. Thoughts with his amazing family & friends RIP."
Former Arsenal and England striker Ian Wright praised the Lowery family, saying: "God bless you, you've done a magnificent job through the plight of your brave boy to bring awareness to this disease. May he rest in peace.X"
Former England striker Gary Lineker, who hosted the Sports Personality Of The Year awards at which Bradley was a special guest last year, said: "Terribly sad to hear that little Bradley Lowery has passed away. A warrior and an inspiration to the end. RIP Bradley."
And Jordan Pickford, the former Sunderland goalkeeper sold to Everton last month for a fee which could rise to Â£30million, posted on Instagram: "Rest in peace Bradley Lowery, such an inspiration to us all #theresonlyone."
Football clubs throughout the country joined in the tributes for Bradley, who died of a rare form of cancer, neuroblastoma, that affects around 100 children a year in the UK.
Newcastle said on Twitter: "Our deepest condolences go out to the family of Bradley Lowery and all who supported him throughout his brave battle."
Liverpool tweeted Bradley had been inspirational, adding: " Our thoughts are with you all at this sad time. May he rest in peace."
Chelsea posted a picture of their players with the young mascot on Twitter and said: "All at Chelsea are deeply saddened to learn of Bradley Lowery's passing. He touched all of us with his bravery and winning smile."
Manchester City posted a picture of manager Pep Guardiola presenting Bradley with a signed shirt and said: "Rest in peace @Bradleysfight (2011-17). Never forgotten."
In March, Bradley accompanied his hero Defoe on to the pitch at Wembley for England's World Cup qualifier against Lithuania and the national team posted a picture of the occasion on Twitter, saying: "T here's only one Bradley Lowery."
Former Nottingham Forest and Liverpool forward Stan Collymore suggested Bradley's life should be celebrated by the game's authorities.
Collymore said on Twitter: "Would love to think @fa and @premierleague could mark @bradleysfight by way of a trophy or award to commemorate."
And former England and Liverpool striker Robbie Fowler tweeted: "Sending our love and deepest sympathies to all of his family, friends and everyone aching by this awful news."
Sunderland forward Fabio Borini, on loan at Inter Mian, posted on Instagram: "Just heard the news about our good friend Bradley. What an amazing contagious smile. True legend to us all. Our love goes to his family and friends and my thoughts are with them during this extremely sad time. #theresonlyonebradleylowery"
Former Manchester United and England defender Rio Ferdinand retweeted the family's notification of Bradley's death and wrote: "Such sad news thoughts are with his family & friends! Godbless lil man"
Tottenham midfielder Victor Wanyama wrote: "Your bravery was an inspiration to many,from me and my family our thoughts are with your family and friends. R.I.P Bradley"
Manchester United and England winger Jesse Lingard posted a picture of Bradley alongside the words: "Thoughts and prayers are with brave little Bradley's family and friends at this sad time #ripchamp"
Stoke forward Bojan Krkic posted: "An exemplary fight, a lesson for life. My condolences to Bradley's family and friends. RIP #OneBradleyLowery"
The Gibraltar Football Association posted: "Rest In Peace Bradley. From the whole of Gibraltar's football family, you touched all of our hearts"
Barcelona and Turkey midfielder Arda Turan wrote: "You touched the hearts of millions. RIP Bradley, brave kid."
Former Real Madrid and Bolton player Ivan Campo said: " The worst news today.Bradley Lowery has died following a brave battle with cancer. RIP"
Wasps playmaker Danny Cipriani tweeted: "Rest in peace Bradley - united fans and people from all over with his fight - respect to JD"
Watford goalkeeper Heurelho Gomes posted: "R.I.P Bradley we love you little angel, my thoughts are with his family."
From the world of politics, Labour leader Jeremy Corbyn wrote: "Heartbreaking to hear that Bradley Lowery has died. I'll never forget images of Defoe & Bradley when he was Sunderland and England's mascot."
Julie Elliott, Labour MP for Sunderland Central tweeted: "Bradley packed so much into his short life. My thoughts are with his family & friends on this very sad day. RIP Bradley Lowery"