Not necessarily. TN requires prearranged professional activity, which may be documented by a detailed employment letter or a contract; an executed statement of work is strong evidence but is not invariably a legal precondition.
Sign first, then apply, then travel
TN requires the professional activity to be prearranged, and official guidance permits that fact to be shown by a detailed employment letter or a contract stating the activities, purpose, anticipated stay, qualifications and remuneration. A signed statement of work is useful in this contractor structure because it confirms the client, deliverables and term, but the law does not make that single document an absolute precondition. The practical sequence is to settle the engagement terms, make the corporation’s support letter consistent with the client evidence, assemble the credential and experience records, and then present the application. Leave time for a request for clearer duties or relationship evidence. If the engagement is later extended, seek an extension before the authorized period ends with updated evidence.
Sequence the file from the actual start date backwards. First obtain the final duties and term, then collect the qualification proof, and only then choose between a CBP admission request and an employer-filed USCIS petition. A loose offer that starts immediately while the documents remain incomplete creates pressure to describe a job before it is settled. Hypothetical example: a dietitian is selected for a twelve-month nutrition-program contract beginning after a hospital expansion. The contract's signed commencement date, rather than a recruiter email, determines when she can sensibly seek TN admission and how long the supporting letter should request.