Hi Poojitha,

As per my understanding, If i am understanding it correctly then it will depend on the condition on business rule is being fired.

Here is below things will matter the most.

1. When criteria(Before,after) since in the data lookup rule you can select on which it should populate to the field like (insert or update).

2. Order- If data look up table is storing the data in order 100 and your custom business rule is setting /changing the value in order 200 then it will override else it will not.

Hope this will make sense.

Regards,

Atul Kumar