In a pre-recorded video posted on social media hours after his arrest, Najib apologized to Malaysians but remained defiant.
Former Malaysian Prime Minister Najib Razak is being investigated over allegations that billions of dollars were looted from a state fund he founded in 2009.
Department director Amar Ishar Singh told reporters that six residences linked to Razak had been raided by the authorities, and that more than $225 million worth of goods were seized.
Mr Najib has been under investigation over the misappropriation of billions of dollars from Malaysia's 1MDB infrastructure fund. Police have also seized jewelry and valuables valued at more than 1.1 billion ringgit ($272 million) from properties linked to Najib, who has denied any wrongdoing.
This story is developing.
The charge against Najib makes Thomas' inaugural case as AG after being appointed to the post on June 5.
"It was the only remaining part of the investigation (following the submission of the) papers (to Thomas on June 13)".
It said in a brief statement that Najib would be brought to court Wednesday to be charged, but didn't give details of the charges against him.
Mahathir Mohamad, Najib's 92-year-old successor who came out of retirement to run for election, told Reuters last month that there was "an nearly flawless case" against the former prime minister.
He and his luxury-loving wife Rosmah Mansor were questioned by investigators, as were his stepson Riza Aziz, whose firm produced the hit 2013 movie "The Wolf of Wall Street", and his former deputy Zahid Hamidi.
Red Granite agreed in March to pay the USA government $US60 million to settle claims it benefited from the 1MDB scandal.
The United States' Department of Justice filed lawsuits to seize about US$1.7 billion in assets that it said had been bought with money misappropriated from 1MDB, including real estate in NY and southern California, artwork, and a luxury yacht.
United States investigators said Najib's associates looted $US4.5 billion from the fund, of which $US681 million landed in Najib's bank account and some $US30 million used to buy jewellery for his wife. Red Granite was unavailable for comment.
The Malaysian government under Najib was accused of blocking probes into 1MDB and not cooperating with foreign agencies investigating the fund, but local probes have been reopened since Mahathir came to power.