After sadly failing in his dream of becoming a jazz clarinettist, Harry Sinclair achieved national prominence as one half of duo The Front Lawn. The group inherited the Blerta tradition of refusing to fit neatly into categories: they combined music, theatre, and comedy. Like Blerta, they also spawned albums and films.

Sinclair's Front Lawn partner, musician Don McGlashan, argued in 1989 that they tried to combine the best bits of theatre and music. "We wanted to bring the excitement of the rock and roll show into theatre."  Mining melodies from Kiwi vernacular ("How are you doing? I haven't seen you for..."), the group also won acclaim in Edinburgh and New York. 1989 saw the release of the first of two albums — Songs from the Front Lawn — plus New Zealand Music Awards for most promising group, best film soundtrack/compilation and international achievement.

Though superstitious about recording any of their theatre performances, The Front Lawn had toyed with turning live show The Reason for Breakfast into a film. Ultimately they abandoned the idea, instead doing a deal with arts show Kaleidoscope which saw them doing an interview, in exchange for borrowing TVNZ resources to make debut short Walkshort (1987). Directed by Bill Toepfer and set entirely on Auckland's Karangahape Road, the film showcased Sinclair and McGlashan in multiple roles.

They followed it by directing and starring in The Lounge Bar (1989) — alongside Lucy Sheehan — which combined two timeframes through the use of song. Then came the Sinclair-directed Linda's Body (1990), by which time actor and singer Jennifer Ward-Lealand had joined the group. The 24-minute tale of romance and ghosts won the Best Short Award at the 1990 NZ Film and TV awards. 

Sinclair and McGlashan's diverging interests saw The Front Lawn increasingly taking a back seat. Sinclair increasingly pursued filmmaking, while McGlashan's work with guitarist David Long on the first Front Lawn album would evolve into beloved Kiwi band, The Mutton Birds.

Sinclair carried on doing occasional acting roles (including a cameo in the opening scene of Peter Jackson's Fellowship of the Ring), but increasingly began to concentrate on film projects. Wary of the traditional approach of writing a script for months on end, then finding actors to play the parts, he "stumbled" across a very different system: he wrote a loose storyline then improvised with camera and actors, before returning to the keyboard. The first result of this new approach emerged as Topless Women Talk about their Lives, a television series made of bite-sized four-minute segments.

In 1997 Sinclair expanded this tale of a group of young Aucklanders into his debut feature. Topless Women played for seven months in local cinemas, won eight NZ Screen Awards (including Best Film, Director and Screenplay), and scored rave reviews across the globe, from the Sydney Morning Herald ("completely seductive because it has such a direct and unpretentious sense of real lives being lived") to London's City Limits ("appealing and ferociously funny") to Screen International ("an energetic, earthy portrait of love and commitment among a group of 20-something friends").

The Price of Milk (2000) was an eccentric follow up, marrying Sinclair's enthusiasm for the surreal tropes of Eastern European cinema with distinctively Kiwi landscapes and characters. The romance paired lovestruck farmers Danielle Cormack and Karl Urban. Milk's stylistic boldness was met with enthusiasm offshore. One enraptured American distributor bought it for release in the United States, where Village Voice called it a "shaggy, appealing parable" which "throws itself onto the magic-realist sword with aplomb". Milk won two awards at Fantasporto in Portugal, and further awards at other fantasy festivals in South Korea and Japan.

Sinclair went on to write and direct Toy Love (2002), out of a desire to "make a really entertaining film that was also a satirical look at male behaviour". Again the film had begun with his cast: "..we looked at all the actors in the country that we found interesting and started working with different combinations of them". Playing the two philanderers were Kate Elliott and Dean O'Gorman. Though a box office disappointment, the film won the Audience Jury Award at Fantasporto in 2003.

Since then Sinclair has been living in the United States. In 2008 he wrote and acted in ambitious multimedia theatrical piece Continuous City. The touring show combined live actors with projected text and videophone messages, and footage shot in Shanghai and Tijuana. 

In 2008 Sinclair married American scriptwriter/producer Rebecca Rand Kirshner (Buffy the Vampire Slayer, Gilmore Girls). Sinclair went on to direct multiple episodes of Kirshner's show 90210. In 2016 he directed short film Everything I Know about Love, in which American writer/actor Winsome Brown plays every role. 

Harry Sinclair is the son of late New Zealand historian Keith Sinclair, and younger brother of playwright/scriptwriter Stephen Sinclair.

Sources include

Peter Calder, 'The Front Lawn on tour - Three for the Road' - The NZ Herald, 26 May 1989, section 2, page 1
Edward Crouse, Review of The Price of Milk - Village Voice, 14 February 2001
Louise Keller, 'Topless Women Talk about their Lives' (Review). Urban Cinefile website. Loaded December 1997. Accessed 14 June 2014  
"Toy Love to premiere in market" - NZ film, No 68, May 2002, page 2