The campaign started in March 2013, after The Royal Parks, which administers London's parks, hired a for-profit company to charge £35 charge per game for groups of eight or more playing in the park.
In September 2013, The Royal Parks announced it would temporarily drop the charges while it carried out a consultation, after the league sought legal advice on the matter.
In August 2013, law firm Leigh Day wrote to the Department for Culture, Media and Sport, arguing that the charges were unlawful, prompting the consultation.
The league set up a petition on Change.org that has received 22,363 signatures and convinced more than 1,000 supporters to respond to The Royal Parks' final consultation.
Following the consultation, the agency announced its decision in a statement on its website: "More than 1,000 people responded with a large majority saying they did not want to see booking or charging of the sites. Following that research we have decided not to charge for these facilities."
The league started in 2003 with just nine teams, but has grown to 80 teams with 10 members in each team.
Vanessa Furey, a league organiser who plays in the Action on Hearing Loss team, said this community was key to the success of its campaign.
She added: "We had an existing network of teams, which was vital in terms of kicking off the campaign."
The campaign also had the support of other groups who use the parks to play group sports, including university groups and hotel group leagues.
To support the campaign on social media, the league created a @saveoursoftball Twitter handle, which has since become a generic handle for the league.
In October last year, the league unveiled a 100ft red ‘For Sale?’ sign in the old football pitches where it plays to highlight that there was a week left on the consultation process.
Furey added: "We’re thrilled we get to start the season without this hanging over us."