He was born at Itzehoe, Holstein, the son of a tradesman, and educated at the Gelehrtenschule des Johanneums. He went to study at Rostock and Helmstedt in 1616, and in 1617 was in Leiden. After a period at Hamburg, where he encountered in particular Holstenius, he returned to Leiden in 1624, where he received a doctorate in law.
Loccenius was recruited by Johan Skytte for Gustavus Adolphus, and went to Sweden. From 1628 to 1642 he taught a humanist and political syllabus as professor skytteanus; from 1634 he also taught Roman law. As librarian also at the University of Uppsala, he received the embassy of Bulstrode Whitelocke, and they discussed English jurists including Francis Bacon and John Selden.
The De jure maritimo was a commentary on Swedish maritime law as published in the Legisterium Sueciæ. As De jure maritimo et navali it went through a number of editions. The maritime law work of Loccenius was later republished, with works by Franz Stypmann and Reinhold Kuricke, by Johann Gottlieb Heineccius. Loccenius wrote in particular on piracy. He was an early author on legal concepts of territorial waters, whose views were quoted long afterwards.
As legal antiquarian Loccenius published an edition of the corpus of Swedish provincial law, the Lex Sueo-Gothorum. His Synopsis juris ad leges Sueticas accommodata (1648) was an early example of the 17th-century use of the Decalogue to classify capital crimes. The Lexicon juris Svevo-Gothicae (1651) was a largely linguistic work.
Loccenius was given the title Rikshistoriograf in 1651. In the 1650s he moved from the study of Swedish medieval law to writing on the general history of Sweden. He initially minimised the pre-Christian period, and he followed Ericus Olai in arguing that foreign kings were responsible for negative aspects of the history. He published:
- Three volumes on Swedish history (1647)
- Rerum Suecicarum Historia (1654)
- Erici Olai Historia Sueicorum Gothorumque (1654)
- Antiquitates Sveo-Gothicae (1670)
- Antiquitatum Sueo-Gothicarum
- idref.fr page.
- John Edwin Sandys (17 February 2011). A History of Classical Scholarship: The Eighteenth Century in Germany and the Nineteenth Century in Europe and the United States of America. Cambridge University Press. p. 10. ISBN 978-1-108-02708-3. Retrieved 17 May 2012.
- Wilhelm Kühlmann; Walter de Gruyter; Achim Aurnhammer; Christine Henschel; Bruno Jahn; Walther Killy (29 September 2010). Kr M Marp (in German). Walter de Gruyter. pp. 464–5. ISBN 978-3-11-022049-0. Retrieved 18 May 2012.
- Literary Relations of England and Scandinavia in the Seventeenth Century. Ayer Publishing. p. 120. GGKEY:DAHXZUCXQY9. Retrieved 18 May 2012.
- Domenico Alberto Azuni (1806). The maritime law of Europe. Printed by G. Forman for I. Riley. p. 407. Retrieved 18 May 2012.
- Franz Stypmann; Reinhold Kuricke; Joannes Loccenius; Johann Gottlieb Heineccius (1740). Ius maritimvm et navticum. sumptibus Orphanotrophei (‘at the expense of the printshop Orphanotropheum’). Retrieved 18 May 2012. Latin in Imprints
- Wilhelm Georg Grewe; Michael Byers (2000). The Epochs of International Law. Walter de Gruyter. p. 307. ISBN 978-3-11-015339-2. Retrieved 18 May 2012.
- Thomas Wemyss Fulton (1911). The Sovereignty of the Sea: An Historical Account of the Claims of England to the Dominion of the British Seas, and of the Evolution of the Territorial Waters, with Special Reference to the Rights of Fishing and the Naval Salute. The Lawbook Exchange, Ltd. p. 550. ISBN 978-1-58477-232-3. Retrieved 18 May 2012.
- Alasdair A. MacDonald; A. H. Huussen (2004). Scholarly Environments: Centres of Learning and Institutional Contexts, 1560-1960. Peeters Publishers. p. 87 note 55. ISBN 978-90-429-1411-7. Retrieved 18 May 2012.
- Virpi Mäkinen (2006). Lutheran Reformation And the Law. BRILL. p. 191. ISBN 978-90-04-14904-5. Retrieved 18 May 2012.
- Jose Rabasa; Masayuki Sato; Edoardo Tortarolo; Daniel Woolf (1 June 2012). The Oxford History of Historical Writing: Volume 3: 1400-1800. Oxford University Press. p. 461. ISBN 978-0-19-921917-9. Retrieved 18 May 2012.
- "Schreiber" (PDF). Retrieved 2012-11-07.
- Johannes Loccenius (1670). Antiquitates Sveo-Gothicae: cum hodiernis institutis comparatae. Retrieved 18 May 2012.
- Literary Relations of England and Scandinavia in the Seventeenth Century. Ayer Publishing. p. 348. GGKEY:DAHXZUCXQY9. Retrieved 18 May 2012.