In 1790 he took control of the family business Jacob Kielland & Søn and soon became one of the wealthiest and most distinguished figures in the city.
His personal success also facilitated the rise to prominence of other members of the Kielland dynasty, who became influential in the commercial, cultural and public life of Stavanger and of Norway for more than a century.
He also conducted several travels to the Nordic countries, the Kingdom of Great Britain and the Dutch Republic, in order to study trade and to build a business network.
The company had benefitted from the French Revolutionary Wars, both from trade, since Denmark-Norway was neutral, and also because Kielland was engaged in insurance and, in this capacity, often made a good return when identifiable flotsam was auctioned.
As the local vice consul for Great Britain from 1787, his intervention was able to secure respect for the neutrality of Denmark-Norway in 1793 and 1796 from British warships.
In 1801, following the Battle of Copenhagen, the United Kingdom and Denmark-Norway became belligerents and it was the vigilantes of Stavanger who set up the city's coastal batteries.
[1] In 1809, Kielland's work during this very difficult time received recognition with the award of: Knight of the Danish Order of the Dannebrog.