Persons granted entry clearance to join a wife/husband/partner, or people in a different category already in the UK, who get married, or civil partnership, or prove two years cohabitation, can be granted leave to remain under Appendix FM of the rules, for a period if two and a half years.
Like all applications, this is a complex area of the law, with strict documentary evidence required.
After five years in this visa category, a person can apply for Indefinite Leave to Remain.