Here's why Mr. White commits suicide in James Bond's Spectre. With No Time To Die delayed due to the ongoing pandemic, 007's most recent cinematic mission remains his 2015 effort, Spectre. Tying together the continuity of Daniel Craig's entire run, Spectre revealed that the villainous Blofeld had been behind everything from the very start, and 007 sets out to defeat his fated villain and foster brother. Spectre also marks the return of Jesper Christensen's Mr. White, who made his Bond debut in Casino Royale. White initially represented the shadowy Quantum organization who were bankrolling Le Chiffre in the film's big poker tournament, and he was later captured and interrogated by 007 in Quantum of Solace.
White returns in Spectre as a changed man. Quantum is revealed to be merely a subdivision of Blofeld's SPECTRE and Mr. White one of the group's many underlings. After Blofeld's tactics became more questionable, White apparently stopped following his boss' orders and incurred the full wrath of the organization, poisoned with thallium via his mobile phone. Bond tracks down his former Quantum enemy, hunting for a lead on Blofeld, and White strikes a deal with the British spy - protect his daughter, Madeleine Swann, and she will lead him to SPECTRE. After 007 agrees, however, White promptly uses James' own gun to commit suicide. The reasoning behind this extreme act of violence is never explicitly addressed, but White's thinking can be more or less completely deduced.
Firstly, it's vital to acknowledge that White is already dying when Bond finds him. SPECTRE's thallium might not be working as quickly as Blofeld had liked (hence why Hinx is sent to finish the job) but the poison is still painfully fatal, guaranteeing White a painful death within the next few weeks. Moreover, White's sole reason for living at this point is to protect his daughter, and this goal is achieved when he arranges for James Bond to act as her protector (and future lover, obviously). After doing all he could to assure Madeleine's safety, White has nothing left to live for other than more lonely days in an isolated cabin, waiting to see whether SPECTRE's assassins or the thallium will get him first.
But White's suicide isn't just about taking control of his inevitable death, it's also the tactical move of a veteran underground criminal. After promising to keep her safe, Mr. White reveals that Madeleine can lead Bond to SPECTRE, but this plan comes with a fatal flaw - why would Bond keep his end of the bargain if he can get the information out of White there and then? While the audience know that the noble 007 would never break a promise (especially one involving an attractive young lady), White comes from a darker world of betrayal and villainy, and gives Bond an incentive to keep his daughter alive. White and Swann are the only two people who have the information 007 wants; by taking his own life, White ensures that the secret agent will stick to his word.
This explanation provides an in-story motivation for Mr. White's suicide, but the storytelling reasons are a little different. By showing Mr. White's brutal death, Spectre drives home to the audience just how dangerous Blofeld's organization is. A once-formidable villain is now cowering in a cabin and choosing to take his own life as the shadow of SPECTRE looms over him. The fall of White only helps elevate Blofeld as Bond's new nemesis. White's death also adds an element of tragedy to Madeleine's character and sets up her romance with James. Both Swann and Bond are lone wolves whose lives were ripped apart by SPECTRE, but they find a measure of solace in each other.
