Complex sentence: He was High Commissioner to Singapore then the Ambassador and Permanent Representative to the Organisation for Economic Co-operation and Development followed by High Commissioner concurrently to Australia, Papua New Guinea, the Solomon Islands and Vanuatu.
Split into simpler sentences: He was High Commissioner to Singapore then the Ambassador and Permanent Representative to the Organisation for Economic Co-operation and Development. Subsequently he became the High Commissioner concurrently to Australia, Papua New Guinea, the Solomon Islands and Vanuatu.