China's Foreign Ministry spokesman Wang Wenbin announced the agreement in Beijing, saying it would involve China cooperating with Honiara on maintaining social order, protecting people's safety, aid, combating natural disasters and helping safeguard national security.
Solomon Islands Foreign Affairs Minister Jeremiah Manele confirmed the signing of the pact to the ABC in a text message.
He said Prime Minister Manasseh Sogavare would make a formal announcement in the coming days.
The announcement comes just days after Australia's Minister for the Pacific Zed Seselja travelled to Honiara and met the country's Prime Minister Manasseh Sogavare in a last-ditch effort to dissuade him from going ahead with the China security deal.
Wang said the cooperation would be transparent and would not target any third party.
"The purpose of China-Solomon security cooperation is to promote social stability and long-term peace and security in Solomon Islands, which is in line with the common interests of Solomon Islands and the South Pacific region," he told a briefing on Tuesday.
"China-Solomon Islands security cooperation is public, transparent, open and inclusive, not directed at any third party, and is parallel to and complementary to the existing bilateral and multilateral security cooperation mechanisms in Solomon Islands.
"China is willing to work with the countries concerned to give full play to their respective advantages and form international synergies."
Earlier on Tuesday, the Solomon Islands parliament was told China would send officials to the Pacific nation next month to sign cooperation agreements.
"The PRC foreign affairs is heading to Honiara in the middle of May to sign multilateral agreements and cooperations with the Solomon Islands government," Douglas Ete, chairman of the public accounts committee, said.
The announcement came only a few days before senior White House official Kurt Campbell was due to visit Honiara as part of a concerted effort by both Australia and the US to dissuade Solomon Islands from pressing ahead with the pact.
On Monday, the US State Department warned that the pact "leaves open the door for the deployment of PRC military forces to the Solomon Islands" and set a "concerning precedent for the wider Pacific island region".
One diplomatic source told the ABC that the announcement was "clearly pushed through" by both countries ahead of Campbell's visit.
Australia's Labor party slammed the Coalition's handling of the issue in the wake of the announcement, with Shadow Foreign Minister Penny Wong accusing the Prime Minister of bungling a key relationship.
"Despite all of his tough talk, on Scott Morrison's watch our region has become less secure," she said on Twitter.
"His government was warned of this security pact in August and he hasn't even bothered to send the Foreign Minister to the Solomon Islands to raise concerns on behalf of all Australians."
Photo file Caption: China's Foreign Ministry spokesman Wang Wenbin