Tilly was educated at Wellington, taking art at Wellington Technical College in the early 1950s. He then attended teachers college in Wellington and Dunedin, specialising in arts and crafts teaching. He was awarded an overseas bursary and studied children"s drama in England during the early 1960s.
On his return to New Zealand he tutored drama and later became a senior acting tutor at New Zealand Drama School. In 1976, Tilly helped establish Wellington"s Circa Theatre, where he acted in a number of plays written by playwright Roger Hall, one of New Zealand"s most successful playwrights. He designed the set for Hall"s breakthrough hit, the public service satire Glide Time, and had starring roles in the follow-up Middle Age Spread and the Hall solo piece C"mon Black.
Aside from a busy stage career, Tilly acted often for the screen.
He made his television debut in the 1967 one-off comedy The Tired Manitoba then ad-libbed alongside playwright Joe Musaphia on the children"s show Joe"s World. Tilly"s biggest screen roles include that of a headmaster who has an affair in 1979"s film adaptation of Middle Age Spread (showbusiness magazine Variety compared him to "an antipodean Woody Allen" ) and in the 1982 comedy Carry Maine Back, as the farmer who must sneak his father"s body back home after he unexpectedly dies.
Grant Tilly"s is the voice in the Oscar-nominated animated Western short The Frog, The Dog, And The Devil. His television credits include an award-winning performance as artist Toss Woollaston in the teleplay Erua, Reverend Henry Williams in the historical epic The Governor, the Margaret Mahy fantasy Cuckooland (1995), and a starring role in 2009 short Roof Rattling.
Tilly also had many smaller parts in feature films, including two adventures shot partly or wholly in New Zealand: he was "The Collector" in the chase movie Race for the Yankee Zephyr, and a villainous German officer in Nate and Hayes (also known as Savage Islands).
Grant also worked as an illustrator and writer for the Wellington newspaper Evening Post, and went on to create artworks encompassing prints, drawing, and three-dimensional artworks made with wood. His “Drawing On History” articles focused on the changing face of Wellington’s urban landscape. In 2002 Tilly, donated his skill to design a flexible 90-seat performance space for Stagecraft Theatre (a non-professional theatre company in Wellington).
In April 2012, Tilly died from prostate and kidney cancer after being bedridden since January.
He was 74 years old and buried in Wellington.
In the 1988 New Year Honours, Tilly was appointed a Member of the Order of the British Empire, for services to the theatre.
