The pay gap between British men and women is at a record low, the government said, with women earning 18 percent less than men in the UK in 2016.
Closing Britain's pay gap could add 150 billion pounds ($187 billion) to the country's annual gross domestic product by 2025, according to consulting firm McKinsey Global Institute.
The new regulations will cover companies with at least 250 workers - which equates to more than 15 million employees or almost half of Britain's workforce, the government said.
Employers must also reveal pay gaps in bonus payments and publish the proportion of male and female staff across each salary bracket, among other requirements.
"We have more women in work, more women-led businesses than ever before and the highest proportion of women on the boards of our biggest companies," said Minister for Women and Equalities Justine Greening in a statement.
"This has helped us to narrow the gender pay gap to a record 18.1 percent – but we want to eliminate it completely."
Other countries to introduce mandatory gender pay gap reporting include Australia, which passed similar legislation in 2012, and Germany, where a forthcoming law will affect companies that have more than 500 employees.
The government said the new law was part of a longer term scheme to support women in the workplace, including investing five million pounds ($6.2 million) to help parents return to work, providing 30 hours of free childcare, and introducing shared parental leave.
Women's rights group Fawcett Society said they "strongly welcome" the gender pay gap reporting legislation.
"Employers should see it as an opportunity not a threat. Through gender pay gap reporting they can address the productivity gap and get the best person for the job at the right level," Sam Smethers, chief executive of Fawcett Society said in a statement.
A parliamentary committee in February said Britain will fail to close the pay gap within a generation as promised without more flexible working, paternal leave, and encouraging women aged over 40 back to work.
On Wednesday, parliament's Business, Energy and Industrial Strategy (BEIS) Committee said that companies should publish pay ratios annually, give workers a seat on the committee that sets pay and have women make up half of all new senior and executive level appointments from 2020.