Couples counseling is not guaranteed, but it is extremely effective with many partnerships. It can help couples get to a great start in discovering a path to the best marriage possible one can have with a spouse. How effective it ends up being will be determined by how much effort you put into it as an individual and also together as a couple. Each partner in the relationship needs to go into counseling sessions with an open mind and heart, and a willingness to communicate honestly. If either one of the spouses or both do not contribute to this then it is very difficult to say whether the sessions will prove to be effective and helpful at all.
Yes, it will work if both partners are on board and want it to succeed. It gives both parties the feeling that someone is listening. A third party can also step in to keep things calm so that progress can be made. The therapist can also ask relevant questions which may help the couple to look at the problems in a different light. Over 90% of couples report that it has helped them. This may not always mean that the couple is encouraged to stay together. The therapy may result in the couple seeing that they are not in a healthy relationship and encourage them to end it.