As a program manager and later office director at the Advanced Research Projects Agency, Roberts and his team created the ARPANET using packet switching techniques invented by British computer scientist Donald Davies and American engineer Paul Baran.

[12] In 1967, although at first reluctant, he was recruited by Robert Taylor in the ARPA Information Processing Techniques Office (IPTO) to become the program manager for the ARPANET.

[15][17] At the Symposium on Operating System Principles (SOSP) that year, Roberts presented the plan based on Clark's message switching proposal.

[18][19][20] There he met a member of Donald Davies's team (Roger Scantlebury) who presented their research on packet switching and suggested it for use in the ARPANET.

[23][24][25][26] Roberts' plan for the ARPANET was the first wide area packet-switching network with distributed control, similar to Donald Davies' 1965 design.

[27] ARPA issued a request for quotation (RFQ) to build the system, which was awarded to Bolt, Beranek and Newman (BBN).

[33] In 1973, Roberts left ARPA to join BBN's effort to commercialize the nascent packet-switching technology in the form of Telenet,[34] the first FCC-licensed public data network in the United States.

Roberts joined the international effort to standardize a protocol for packet switching based on virtual circuits shortly before it was finalized.

[41] Roberts claimed in later years that, by the time of the October 1967 SOSP, he already had the concept of packet switching in mind (although not yet named and not written down in his paper published at the conference, which a number of sources describe as "vague").

[42][43][44][45][46] Furthermore, he claimed that his experiment with Thomas Marill in October 1965,[47] was based on packet switching;[48][49][50] and that their subsequent paper, Towards a Cooperative Network of Time-Shared Computers, published the following year, was a blueprint for the ARPANET.

[60] His early work, prior to SOSP, has been described as "extend[ing] the concept of a support graphics processor to the idea of a network" using "existing telegraphic techniques".

[61][62] Primary sources and historians recognize Baran and Davies for independently inventing the concept of digital packet switching used in modern computer networking including the ARPANET and the Internet.