In 2014, during the most prestigious freediving competition in the world, Vertical Blue, which takes place in the Bahamas, Marianna Gillespie imposed herself on the international scene, reaching, in constant weight with monofin, a depth of -86 meters, thus winning a silver medal. During the same tournament, she won two more medals: gold in free immersion and silver in constant weight without fins. In the same year, she became World Champion by team. In 2015, her results ensured her, once again, the rank of World No. 1, all disciplines combined. In 2016, Marianna decided to continue her progression in depth, focusing on the discipline of constant weight with monofin and reached -93 meters, thus taking 4th place in the world in the discipline. That same year, she also brought a bronze medal to her team at the Team World Championship. In 2018, during the Sabang International Freediving Competition, the cumulative results she obtained in the three freediving disciplines, depth category, positioned her 6th place in the world ranking. In 2019, at the World Championship in Villefranche-sur-Mer, Marianna competed in all individual events and won the gold medal in free immersion and two silver medals in constant weight with monofin and without fins. She was titled best athlete of championship and took the position of World No. 1 in the depth category.