Girlguiding UK found they needed a new vow that includes non-religious members and those who follow other faiths.
It has been replaced with a new promise to "be true to myself and develop my beliefs".
The new oath drops the reference to God for the first time since Guides began in 1910.
Brownies and Guides currently vow to "to love my God, to serve my Queen and my country".
I promise that I will do my best
To be true to myself and develop my beliefs
To serve the Queen and my community
To help other people
and
To keep the Guide (Brownie) law
The consultation about the vow was carried out earlier this year and involved nearly 44,000 Girlguiding UK members and non-members.
Chief Guide Gill Slocombe said: "Guiding believes in having one promise that is a clear statement of our core values for all our members to commit to. We hope that our new promise will allow all girls - of all faiths and none - to understand and feel proud of their commitment."

Daniel Bragg, 37, hit Julie Cook, 44, so hard he broke her left eye socket in the assault, police said.
Ms Cook fell and hit her head on the floor, causing a serious injury. She died in hospital two days later.
Bragg, who admitted manslaughter, was sentenced to five years and four months in prison.
He initially denied the killing, but changed his plea on the second day of his trial at Winchester Crown Court.
Bragg was overheard by friends four days before Ms Cook was killed saying "one of these days I'm going to kill her", Dorset Police said.
A Domestic Violence Protection Order had been made against Mr Bragg in April stopping him from contacting or going to Ms Cook's home, the force said.
However, the couple, from Bournemouth, remained in contact and on 28 April 2016 - just four days before the assault - a friend of the couple heard Mr Bragg say something to the effect of "if we carry on like this I will end up killing her".
The couple had been at Pokesdown Railway Station when they started arguing and Ms Cook walked away.
After punching her, Bragg initially walked away but returned to help Ms Cook, who was unconscious on the concrete platform, and took her back to her flat.
The couple had been together for about four years before the incident and their relationship was described as "volatile".
Det Insp Neil Phillips said: "There was no justification for such violence. Bragg and Julie clearly had a volatile relationship and efforts had been made to prevent further abuse.
"However, Julie and Bragg continued to maintain contact and she tragically died as a result of his violent behaviour."

The Hydrus Group, an oil and gas service company, has started work on a specialist manufacturing base at the Brechin Business Park.
It is forecast the new development will bring tens of millions of pounds into the local economy.
The new facility should be complete by spring 2015 and bosses say it will create 100 jobs over five years.
Hydrus presently employs 50 people in Brechin at a site on Eastmill Road, which will trade in tandem with the new premises.
The facility will include capacity for specialist engineering structures to be built on site, ready for export.
Mark Williams of Hydrus said it was a "natural step" for the firm to expand in the area.
He said: "The growth of the energy sector in Aberdeen is spilling over into Angus for the area's benefit.
"Brechin is a great location for us. We are creating huge structures for the oil and gas sector.
"Good transportation links are essential, so the proximity of the deep sea access at Montrose Port is a significant benefit, particularly as we look to expand our export markets."
Angus provost Helen Oswald said the new facility was "great news for Hydrus and the county".
She said: "Angus Council is delighted to be working with such an innovative company, whose enterprise and ambition is bringing jobs and economic benefit to Angus."
From September, girls joining the Brownies and Guides in the UK, will no longer have to pledge their devotion to God.
[NEXT_CONCEPT]
A man who punched and killed his girlfriend just days after he was overheard saying he would kill her has been jailed.
[NEXT_CONCEPT]
An engineering firm is to build a new technology centre in Brechin, creating 100 new jobs.