Mrs May, who's a Christian, said the money would be targeted at dealing with the routes of the people trafficking trade in countries like Nigeria, as she unveiled a new taskforce which is to co-ordinate the Government response to slavery. The Prime Minister will chair the taskforce.
Ministers estimate there are between 10,000 to 13,000 potential victims of slavery in the UK.
The global trade in people is estimated to cost £113 billion, with human trafficking for sexual exploitation believed to cost the UK £890 million.
A review by barrister Caroline Haughey to mark the first anniversary of the Modern Slavery Act found 289 modern slavery offences were prosecuted in 2015, with a 40% rise in the number of victims referred for support.
The Government has also asked Her Majesty's Inspectorate of Constabulary (HMIC) to assess the police response to modern slavery.
Mrs May said: "This Government is determined to build a Great Britain that works for everyone and will not tolerate modern slavery, an evil trade that shatters victims' lives and traps them in a cycle of abuse.
"Last year I introduced the world-leading Modern Slavery Act to send the strongest possible signal that victims were not alone and that those responsible for this vile exploitation would face justice.
"We must do more and the historic £33.5 million funding will allow us to go even further to support victims.
"Alongside this, the Haughey and HMIC reviews send a clear message that the criminal justice system must ensure that perpetrators have nowhere left to hide.
"I am pleased to see progress but we will not stop until slavery is consigned to the history books."
