People who have leave to enter or remain in the United Kingdom as a spouse of a person present and settled in the United Kingdom are eligible to apply for indefinite leave to remain prior to their probationary period expiring.
If you were granted entry clearance or leave to remain as a spouse under the old rules (i.e. your application was submitted prior to 9 July 2012) then you are eligible to apply for indefinite leave to remain after you have completed two years lawful residence in the United Kingdom. If you applied for your spouse visa after 9 July 2012 then you are eligible to apply for indefinite leave to remain up to 28 days prior to completing the five year probationary period .
Since 28th October 2013 as part of the requirement for indefinite leave to remain you are required to pass the Life in the UK test and also need to pass a level B1 English course.