He served in various capacities at the Serafimerlasarettet in Stockholm, and participated as ship surgeon aboard the corvette "Jarramas” on its expedition in the Mediterranean Sea during 1839–40.

Regnell was born in Stockholm, Sweden, but because of poor health, he suffered from a serious lung disease.

He left Sweden for Brazil in 1840 and settled in Caldas, in the province of Minas Gerais, where he spent the rest of his life.

There Regnell acquired considerable reputation as a practicing physician and consequently a substantial fortune.

Having accumulated considerable wealth, he financially supported several European botanists and donated large sums to various scientific institutions at home.