Kwok was kidnapped by the notorious gangster "Big Spender" Cheung Tze-keung on 30 September 1997, and was released seven days later without police intervention. Negotiations fronted by wife Wendy resulted in payment of a ransom rumoured to have been in nine figures. Following his arrest in Guangzhou in 1998, Cheung confessed that he had put Kwok in a wooden container blindfolded for four days, and fed him regular meals of roast pork with rice, until the ransom of some HK$600 million was paid. The ransom in 1,000-dollar notes was packed inside 20 large carrier bags and driven in two Mercedes saloon cars to a quiet lane in Central district. After the kidnap, the badly shaken Walter handed over the executive duties of SHKP to his younger brothers while retaining the title of chairman and chief executive. His abductor was executed in the People's Republic of China in December 1998.

Sing Tao Daily and sister publication The Standard reported that matriarch Mrs. Kwok Kwong Siu-hing, wielding the holding of the Sun Hung Kai trust, intervened to oust Walter from his chairman position to protect the family's interests. It was revealed that Ida's influence, through being Walter's mistress of four years, has been causing friction with his brothers. On 29 February, tycoon and fellow board member Lee Shau Kee confirmed that, during the last board meeting, Mrs Kwok had forced the leave of absence on Walter. Lee further painted a picture of a lonely Walter, as only Ida would Listen to him. In mid May 2008, Walter brought a lawsuit against his brothers, and persuaded a judge to enjoin a board meeting, saying that Raymond and Thomas had him diagnosed as bipolar disorder to sideline him and silence his criticism of certain Business decisions.

Walter, formerly chairman and CEO of that organisation, negotiated his departure from the family firm in 2010. His mother remains the controlling shareholder of the company, whilst his brothers manage the firm. The Kwok brothers are the third wealthiest people in Hong Kong and Greater China Region, just after Li Ka Shing and Lee Shau Kee. The Kwok family is the third richest family in Asia, with a net worth of US$40.4 billion as of 2018.

In 2012, younger brothers Thomas and Raymond, as well as Rafael Hui, previously the second-highest ranking government official in Hong Kong, were arrested by the city's anti-corruption agency on suspicion of bribery. It has been suggested that Walter, who was not arrested, was the one who passed information to the authorities, supposedly in revenge for his ouster from Sun Hung Kai Properties a few years earlier.

Walter Kwok, Thomas Kwok and Raymond Kwok are together referred to by financial and mainstream media as the Kwok brothers. Together they control the majority of Sun Hung Kai Properties, the largest real estate company in Asia. As of 2015, all three brothers were listed by Forbes in the Forbes 500 listing of the richest people in the world, with a combined net worth of $19 billion (as of August 2015).