Speaking outside Downing Street amid heavy rain, Ms Truss said she had “three early priorities”, which were growing the economy, helping with energy bills, and getting the UK working.
She said: “Firstly, I will get Britain working again. I have a bold plan to grow the economy through tax cuts and reform.
“I will cut taxes to reward hard work and boost business-led growth and investment.
“I will drive reform in my mission to get the United Kingdom working, building and growing.
“We will get spades in the ground to make sure people are not facing unaffordable energy bills and we will also make sure that we are building hospitals, schools, roads and broadband.
“I’m confident that together we can ride out the storm, we can rebuild our economy and we can become the modern brilliant Britain that I know we can be.
“This is our vital mission to ensure opportunity and prosperity for all people and future generations. I’m determined to deliver.”
The new Prime Minister added the country needs to build “roads, homes and broadband faster” with more investment in towns and cities across the country.
She said: “I know that we have to tackle those challenges. Of course it won’t be easy but we can do it. We will transform Britain into an aspiration nation.
“I will take action this day and every day to make it happen.”`
Her speech was drowned out at time by protesters playing loud music including the song Mad World from the streets surrounding Downing Street.
Chanting from protesters and an air horn could also be heard as she delivered her maiden speech.