ISO 17025 calls for you to "verify" the method first. The verification for a laboratory developed procedure includes specifying it to the customer and getting their approval (7.2.1.4), verifying that you can perform the procedure (7.1.2.5), and that the development of the method follows the requirements in 7.2.1.6.
The validation process is where you prove that your method produces acceptable results (7.2.2.1)