If you have already entered into a marriage or Civil Partnership, you can apply to join your settled spouse or Civil Partner in the UK (i.e. that they hold Indefinite Leave to Remain or British Citizenship). You will need to prove:
Proving to the Entry Clearance Officer that you have an intention to live together with your husband, wife or Civil Partner is certainly not straight forward. The Entry Clearance Officer will look into your relationship before and since your marriage or Civil Partnership.
If you are already in the UK and wish to marry or enter into a Civil Partnership, you may be able to apply to the Home Office for a Certificate of Approval. This will give you the permission you need to marry or enter into a Civil Partnership in the UK.
If you are not eligible to apply for a Certificate of Approval under your current status in the UK, you will have to return to your country of origin and decide whether to return as a spouse or Civil Partner or as a fiancé/fiancée or proposed Civil Partner. This will ultimately depend on where you wish for your marriage or Civil Partnership to take place.
If your application as a spouse or Civil Partner is approved, you will be granted leave to enter or remain in the UK for a two-year probationary period. After the two-year probationary period under this category, you may be eligible to apply for Indefinite Leave to Remain.
You may be able to apply as the spouse or Civil Partner of a person with limited leave to remain in the UK but, this will depend on the basis of their stay in the UK.