"The changes were introduced to create more meaningful contests, elevate competitive standards, strengthen the competitive structure of both events, and enhance the tournament experience for athletes and fans," cricket's international governing body said in the wake of weekend board meetings.
The traditional World Cup - which features one-day internationals - is usually staged every four years. Australia are defending champions after beating India in the final at Ahmedabad in a 10-team tournament in 2023.
Next year's edition will involve 14 teams and be co-hosted by South Africa, Zimbabwe and Namibia.
The T20 World Cup is usually staged once every two years, and India are the defending champions after winning on home soil in March.
Changes to the 2027 World Cup:
Round 1: The teams in the 12th, 13th and 14th qualifying places will contest a so-called "Super Series" round, the winners advancing to join 11 other teams in the group stage.
Round 2: Twelve teams will be divided into two groups of six. The top three from each group in the league stage will advance - along with the best fourth-placed team - to the Super 7 stage.
Round 3: The Super 7 includes a round-robin format, with each team playing six rivals and the top four advancing to the knockout stage. Semi-finals: No.1 vs No.4, No.2 vs No.3.
"The structure has been designed to strengthen the competitive narrative across every stage of the event," the ICC said.
Changes to the 2028 T20 World Cup:
The tournament in Australia and New Zealand will feature 20 teams and have 30 matches in the initial group stage.
Group stage: Teams will be divided into five groups of four. In the previous T20 World Cup, there were four groups of five teams. The top two from each group will advance.
Super 10: This round will have two groups of five, playing a round-robin format. Winners of each will qualify directly for the semi-finals. The remaining two semi-final spots will be decided through a new eliminators round, with the second-placed team from each Super 10 group facing the third-placed team from the opposite group. Winners of those eliminators will complete the semi-final line-up.
Twelve teams - Afghanistan, Australia, Bangladesh, England, India, Ireland, New Zealand, Pakistan, South Africa, Sri Lanka, West Indies and Zimbabwe - have already made it to the 2028 event, based on performances in the 2026 T20 World Cup and team rankings.
The remaining eight spots at the 2028 edition will be filled through a 16-team global qualifier competition.
The US, Canada, Italy, Namibia, Nepal, the Netherlands, Oman and the United Arab Emirates got automatic places at the global qualifier. Scotland have direct entry into Europe's regional final.
