JDR will help on the pre-commissioning, testing and termination stages of the project, located 32 kilometres from the German coast.
The UK firm's previous contract for the project included onshore planning and procedures, mechanical installation and cable containment.
Siem Offshore was contracted by project developer EnBW to provide the project's inter array cabling in 2013. More than three quarters of the inter array cables have been put in place.
EnBW installed Baltic 2's substation in October and 80 Siemens 3.6MW turbines are in the process of being built. The project is due to be commissioned later this year.
Siem and JDR have formed a close relationship in the offshore sector. Siem also contracted JDR to manufacture the cables for the 332MW Nordsee 1 project, being developed by RWE.