On February 3, 1885, Lavell became Warden of Kingston Penitentiary, a post he reluctantly accepted. He lived in Cedarhedge with his wife, Betsy, and their 10 children.
In 1885, Prime Minister Macdonald asked Dr. Lavell and Dr Valade (of Montreal) to examine Louis Riel. Riel had been sentenced to death because of an uprising he had led. The doctors were to determine whether Riel was "…so bereft of his reason as not to know right from wrong and as not to be an accountable being" . Dr. Lavell found that "Riel, although holding and expressing foolish & peculiar views as to religion and general government, is an accountable being and capable of distinguishing right from wrong". As a result, the sentence of death was carried out. Lavell himself died in Kingston in 1901