This post has been updated as per the GST Council’s decision to exempt interstate service suppliers from mandatory registration.
Under GST, certain persons have to compulsorily register, irrespective of their turnover. This means that such persons should register even if their turnover does not cross the threshold limit of Rs. 10 Lakhs for special category states and Rs. 20 Lakhs for rest of India. These persons are:

Persons Nature of activities
Persons making interstate supplies All persons who make interstate outward supplies of goods have to mandatorily register. Note that exports and imports are also considered as interstate supplies.

As per the GST Council’s decision, service providers supplying interstate services have been exempted from mandatory registration w.e.f. 13th October, ’17.

Persons making taxable supplies on behalf of other taxable persons Example: Agents, brokers, dealers, etc. who make taxable supplies on behalf of other taxable persons.
Persons liable to pay tax on reverse charge Read this blog post to know more about the supplies on which reverse charge is applicable
Casual taxable persons These are persons who occasionally undertake taxable transactions in a state where they do not have a fixed place of business. For example, sellers in exhibitions, trade fairs, circus business, etc.

Read more about casual taxable persons

Non-resident taxable persons These are persons who reside outside India and occasionally undertake taxable transactions in India, where they do not have a fixed place of business or residence.

Read more about non-resident taxable persons

Input service distributors An input service distributor is an office of a supplier of goods and/or services, which receives tax invoices for inward supply of services, and distributes input credit on these invoices to offices registered under the same PAN.

Read more about input service distributors

Persons liable to deduct TDS Departments or establishments of the Central and State Governments, local authorities and governmental agencies are liable to deduct TDS on inward supplies.

As TDS rules have been deferred currently, mandatory registration is not applicable to these persons till the TDS rules are made applicable.

Persons making supplies through e-commerce operators All persons making supplies through e-commerce operators should mandatorily register.

As TCS rules have been deferred currently, mandatory registration is not applicable to these persons till the TCS rules are made applicable.

E-commerce operators An e-commerce operator is a person who owns, operates or manages a digital or electronic facility or platform for e-commerce.

As TCS rules have been deferred currently, mandatory registration is not applicable to these persons till the TCS rules are made applicable.

Persons supplying online information and database access or retrieval services from a place outside India to a person in India For example: Persons providing e-books, cloud services, online downloading of software, advertising space on a website, etc. from a place outside India to a person in India.

Credits: Tally Solutions

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