"The colonists came here to make a new future for themselves and their families. They wanted land and many were impatient or ignorant of the Treaty, which they saw as an impediment to the march of progress."
She said successive governments supported those colonists' demands.
"In 1840, Maori could not have imagined the scale of the colonisation that was to come. They protested against breaches of the Treaty - to no avail - and their resistance culminated in armed conflict."
Reddy said that despite its fraught history and uncertain legal status, the Treaty was a "living document and a vital part of our constitutional framework".
"It is central to our history - and we live with that history. Every community in New Zealand is the way it is today because of that document and the aftermath of those signings 177 years ago today."
She said Waitangi Day meant different things to different people.
"If I were to ask them what Te Tiriti o Waitangi - the Treaty of Waitangi - means to them, there would be a mixed response, ranging from an instrument of colonisation - or a musty 19th century relic - to a solemn pact between two peoples about how they were to live together in the future."
However, Reddy said she had been fortunate to witness a shift in perceptions about the Treaty and an acknowledgement of "the systematic denial of those promises over time".
The Treaty settlement process had allowed for confidence in a better future. "Our Treaty asked of us that we act in good faith and value each other's rights and respect difference. Those are qualities to value and affirm."
The event was attended by Prime Minister Bill English and numerous other MPs, diplomats and dignitaries.
Just before the garden party, Reddy presided over a citizenship ceremony, and the newly fledged citizens also stayed on for the event.