More than 60,000 people have been killed in the three-decades-old conflict for a Tamil homeland on the Sinhalese-majority island.
Yasushi Akashi, who arrived in Colombo late Sunday, began his peace bid amid continued shelling overnight between the government and Liberation Tigers of Tamil Eelam (LTTE).
He first met with Sri Lanka's former chief peace negotiator Nimal Siripala de Silva, and was to hold talks with other Colombo-based political parties later in the day, government officials said.
Akashi is also expected to meet top LTTE leaders during his six-day visit, although a sit-down with the Tiger's reclusive commander Velupillai Prabhakaran is unlikely.
The envoy would "exchange views on the peace process and its future with leaders of political parties, international organisations and others," the Japanese embassy said in a statement.
His arrival is the first of several by foreign envoys this week as the international community struggles to keep planned peace talks on October 28-29 i