Scottish League One clubs will play a 27-game season starting on October 17, with sides due to play each other three times instead of four.
The move - confirmed by the SPFL on Thursday after it was voted on by League One sides - will see the third tier of Scottish football mirror the Scottish Championship.
Discussions are ongoing regarding the fixture programme for Scottish League Two in 2020/21.
Neil Doncaster, chief executive of the SPFL, said: "Following a period of consultation with all League One clubs, they have today formally voted to approve the altered programme for the 2020/21 season.
"This is positive news and gives clubs a greater level of clarity and, crucially, a target date to aim for.
"Of course, the safety of players and staff at all of the clubs involved will remain paramount, with these dates still contingent on the continued reduction in the virus's spread.
"Now that we know what next season will look like for League One, work will begin on compiling the competition's fixture list."
League Two clubs also voted to approve a 27-game fixture calendar for the 2020/21 season on Friday.
The decision means each of the SPFL's four divisions now has a proposed starting date to work towards, with the Premiership due to begin on August 1 and the other three tiers set to return to action on October 17.