Sweeping reforms that will modernise life and trade in Saudi Arabia will be delivered with British support, Theresa May has announced.
Over the next 13 years the kingdom wants to reduce its reliance on oil exports, increase the number of women in work and boost access to culture.
The state has long-faced protests over its poor record on women's rights and is facing intense condemnation over its military action in Yemen.
Mrs May has made clear she intends to engage with the kingdom rather than "standing on the sidelines and sniping".
She will meet King Salman on Wednesday to sign Britain up as a leading partner in the Vision 2030 programme.
Mrs May said: "These new partnerships, on defence and security, trade and the economy, education, healthcare, culture and sport, evidence the breadth and depth of the UK's relationship with Saudi Arabia.
"We are firm supporters of Saudi Arabia's Vision 2030, an ambitious blueprint for internal reform that aims to deliver greater inclusivity for all Saudi citizens, something we agree is essential to Saudi Arabia's long-term stability and success.
"As a world leader across a range of sectors, the UK is well placed to help Saudi Arabia deliver these vital reforms."
In the meeting, the PM and the king will agree to talks between foreign and trade ministers every six months to build on security and defence work between the countries.
The UK will help to reform the Saudi Ministry of Defence, including reviewing capabilities.
UK tax experts will help Saudi Arabia to diversify its economy and become less reliant on oil and the countries will share information on the best health and education practices.
Saudi's reform programme includes plans to boost the proportion of women who work from 22% to 30% and increase household spending on culture and entertainments.
Mrs May is also holding talks with Princess Reema, vice-president of the Saudi General Sports Authority.
The UK will back plans to encourage more men and women to take part in sport.
Conservative clerics in the kingdom oppose physical education for girls as "immodest" and the subject has not been on the school curriculum.
Princess Reema is a graduate of George Washington University and served as chief executive officer of Harvey Nichols in Riyadh.