The two parts of the title describe two different things. "Head of the Federal Chancellery" is an administrative function: the person who leads the Chancellery as an authority on the Chancellor's behalf, directs its staff and organises its work. "Federal Minister for Special Tasks" is a constitutional status: it makes the office-holder a member of the federal government with a seat and a vote in cabinet, without assigning a ministry of their own.
The combination is a choice, not a constitutional requirement. Since the 1980s most chancellors have given their chief of staff ministerial rank, but some have preferred a senior civil servant: Frank-Walter Steinmeier, for example, headed the Chancellery under Gerhard Schröder from 1999 to 2005 as a state secretary. Ministerial rank gives the head more political weight — at the cabinet table, in coalition talks and in parliament — while the civil-service model keeps the office more clearly administrative.
What the title does not create is a hierarchy over other ministers. The Head of the Chancellery is not the Chancellor's deputy; that role belongs to the Vice-Chancellor under Article 69. Nor does the office confer a right to direct other departments. Its authority is borrowed: it comes from the Chancellor's guideline competence and from the procedural position the Chancellery holds in the government's rules of procedure.
Procedural levers
Those rules are concrete. Under the Joint Rules of Procedure of the Federal Ministries (GGO), draft cabinet submissions are addressed to the Head of the Federal Chancellery (§ 23(1)) and should normally arrive at least eight days before the cabinet deliberates (§ 23(3)). Ministries must inform the Chancellery early about all matters of fundamental political importance (§ 24(1)) and must notify it as soon as a bill is being drafted, keeping it updated on progress and timetable (§ 40). For bills of particular political significance, the Chancellery's consent is needed before a draft is sent out to the Länder and associations (§ 47(2)). None of this is a veto over content — but it gives the Chancellery visibility over the whole legislative pipeline.