Citizens from Saudi Arabia and Bahrain join those from other GCC states including Kuwait, the UAE and Qatar in being eligible.
From June 1, nationals of the two countries can apply to travel to the UK for tourism, business, study or medical treatment for up to six months online before travel without needing to submit visa applications.
UK ambassador to Saudi Arabia Neil Crompton said the process was quick, straightforward and inexpensive.
An electronic visa waiver will cost only about 140 Saudi riyals ($37), the Saudi Press Agency reported. That is around a third of the old price of $128 for six months.
UK Home Secretary Priti Patel said the visa waiver for Saudi Arabia will “connect the people of our countries and boost economic prosperity”.
“The electronic visa waiver is a quick, digital alternative to the regular visit visa and ensures all the necessary security checks are carried out in advance of travel. The visa improvements announced today will provide greater security for our citizens while making it easier and cheaper for visitors from the Gulf to travel here for leisure and business,” she said.
The electronic visa waiver will allow Saudis and Bahrainis to travel to the UK without obtaining a prior visa provided they complete an online waiver form and pay the fees.
The UK Home Office said the process is faster than applying for a visa as there is no need to provide biometric information, visit a visa application centre or hand in your passport before travel.
Foreign Secretary Liz Truss said the visa waiver will strengthen the UK's relationship with Saudi Arabia and Bahrain, making it easier for visitors from the Gulf to come to the UK.
“Our friendships with both countries are of great importance, built on shared priorities such as trade, investment and security,” she said.