Sadler's interest in astronomy developed when she was eight years old and received a book with photographs of telescopes and the Universe, which "got [her] thinking about big questions."[7] At age 11, she joined the local amateur astronomical society in Guildford, England, where she was the youngest member.[7]
Sadler studied physics at the University of Queensland, where she received her undergraduate degree.[8] She received her PhD in astronomy from Australian National University in 1983.[8][7] Following graduation, she worked at the European Southern Observatory and Kitt Peak National Observatory before moving to the Australian Astronomical Observatory.[7] In 1993, she began working at the University of Sydney. Receiving three ARC Fellowships, she "had time to carry out research projects with a broad scope."[7] With a team of colleagues, Sadler developed a radio atlas of the entire southern sky, using the University of Sydney's Molonglo Observatory Synthesis Telescope, which is now used by astronomers internationally.[7]
In her role directing CAASTRO, she oversaw "a network of over 100 scientists and more than 40 research students across CAASTRO's seven university nodes (at the University of Sydney, Australia National University, Curtin University, University of Melbourne, University of Queensland, Swinburne University of Technology and University of Western Australia) and eleven Australian and overseas partner institutions."[4]
In July 2015, Sadler's research team found a 5-billion-year-old galaxy using the CSIRO's Australian Square Kilometre Array Pathfinder.[9]
Sadler's primary research areas include galaxy evolution and active galaxies.[4]