Sabinus Theodor William Halvor Seidelin (29 April 1819 – 29 October 1904) was a Danish businessman and landowner.

In 1834, Seidelin became an apprentice under merchant Vitus Ingerslev (1801–77) in Aarhus; after completing his apprenticeship, he worked for the firm for a few more years.

[2] On 29 May 1856, it relocated to Copenhagen where Seidelin purchased Moses & Søn G. Melchior's property at Amagertorv 11.

He is one of the men seen in Peder Severin Krøyer's monumental 1905 group portrait painting From Copenhagen Stock Exchange (Børsen).

[1] Seidelin died on 29 October 1904 at Lönstorp in Scania and is buried in the Garrison Cemetery in Copenhagen.