A billiard room and ballroom, designed by Rees and Patterson, was added to the rear in 1882-83.
In 1880 the property passed to John William Downer. Born in Adelaide in 1844, Downer was from a family of talented lawyers and legislators. He was called to the bar in 1867, became a Queens Counsel in 1878, and practised with his brother Alexander George Downer. Downer was the MP for Barossa from 1878 to 1901, attorney general in the Bray ministry from 1881-84, premier and attorney general from June 1885 to June 1887, premier from October 1892 to May, 1893, chief secretary in 1892-93 and treasurer in 1893.
Most importantly, he was a member of the Federal Conventions of 1891 and 1897-98, which considered and finally drew up the commonwealth constitution. He was a South Australian senator in the first commonwealth parliament 1901-03 and state MLC from 1905 till his death in Adelaide in 1915.
The property remained in the Downer family until 1924, when St Mark’s bought it for use as a residential college of the University of Adelaide.