The change is part of ITF's aim to bring the international team competitions in women's and men's tennis closer together.
To make the transition, the 2025 Billie Jean King Cup qualifiers will be played across seven group events in April, consisting of three teams in each group, ITF said.
Each three-day event will be held in one location and played on a round-robin basis. The seven group winners will join a host nation in the finals.
Home-or-away ties will return in the qualifiers from 2026 onwards, ITF added.
In the 2025 Davis Cup, meanwhile, the September stage will move to seven home-or-away ties played over two days from four group stage events played over six days. The seven winning teams will join a host nation in the Final 8 in November.
"I am excited for the future of both competitions," said ITF President David Haggerty.
"The format amendments aim to build on the success we have seen across both events in recent years and contributes towards our long-term ambition to bring them more in sync under the World Cup of Tennis banner.
"In Billie Jean King Cup, the move to an eight-team Finals aligns with the Davis Cup Final 8 format which has proven to be such a success.
"Moving the Davis Cup September stage from six-day group stage events to two-day home-or-away ties will ease players' schedules immediately following the US Open, while maintaining the intensity of the competition that they all love."
The 2024 editions of both events are being held in Malaga, Spain.