If you are referring to the act as a whole, and you introduce it in your sentence, you should put the title and year in italics, e.g.
The Matrimonial Law Act 1973 considers the welfare of the child.
If you are referring to a particular section/part/etc. of the act you would include this information in round brackets after the title, e.g.
The Matrimonial Law Act 1973 (s.25) states the first consideration...
Alternatively, if you would rather keep the name of the act as an in-text citation you would need to rearrange the sentence, e.g.
The legislation (Matrimonial Law Act 1973) states....
