The main function of the Department of the Legal Draftsman is the drafting and amending of legislation and the drafting and revision of subsidiary legislation in order to facilitate the successful implementation of the Governments legislative programme. The Governments legislative programme is structured in such a manner so as to successfully implement the policies of the government, which are embodied in the decisions of the Cabinet of Ministers. It is therefore the primary duty of the Department of the Legal Draftsman to provide the necessary domestic legal infrastructure in order to facilitate such implementation. The Department of the Legal Draftsman is also required in the discharge of its functions, to prepare legislation in both the official languages, i.e. Sinhala and Tamil, as well as in English which is the link language.

In carrying out the function of drafting legislation the Department is governed by the provisions of the Constitution of the Democratic Socialist Republic of Sri Lanka and the Administrative Regulations which have been framed for such purpose and which are embodied in the Establishments Code, which Code is issued under the directions of the Cabinet of Ministers by the Ministry of Public Administration. Article 75 of the Constitution states that Parliament shall have the power to make laws. Articles 76 to 80 set out the procedure applicable to the exercise of the legislative power of Parliament. The Establishments Code in Chapter XXXIII 2:1 to 2: 3 deals with Draft Legislation and it states that, "a request for a draft of legislation should in all cases be accompanied by a memorandum containing the fullest possible instructions for the assistance of the Legal Draftsman, in the preparation of the draft" and upon the Cabinet determination has been made on the governments programme of legislation, such conclusion shall be communicated to each Secretary and the Legal Draftsman. In relation to subordinate legislation it is stated that such "subordinate legislation should drafted by the Ministry or Authority which requests the same, and thereafter be forwarded to the Legal Draftsman for revision and be in duplicate and in all three languages".

The Department is also called upon to express opinions with respect to draft legislation and subsidiary legislation and has also to co-ordinate with Parliament for the successful enactment of legislation drafted in conformity with the provisions of the Constitution.