The title Viscount Newcomen was created in 1803 for the wife of the first Baronet Gleadowe-Newcomen. Their son inherited the baronetcy in 1807, then the viscountcy in 1817. Both titles became extinct upon the death of the second viscount in 1825.

Baronets Gleadowe-Newcomen of Carrickglass (1781)

• Sir William Gleadowe-Newcomen, 1st Baronet (d. 1807)
• Sir Thomas Gleadowe-Newcomen, 2nd Baronet (1776–1825), succeeded as Viscount Newcomen in 1817.

Viscounts Newcomen (1803)

• Charlotte Gleadowe-Newcomen, 1st Viscountess Newcomen (d. 1817)
• Thomas Gleadowe-Newcomen, 2nd Viscount Newcomen (1776–1825)