Introduction Young people use social media to communicate about self-harm and suicide and this is associated with both potential risks and protective effects. The #chatsafe guidelines were originally developed in 2018 to equip young people to communicate safely online about suicide. They were shown to be safe, acceptable, and beneficial; however, they do not provide guidance on self-harm, and social media is constantly evolving. This study aimed to update the #chatsafe guidelines to reflect new evidence and current social media affordances, and to include guidance on self-harm. Methods A Delphi expert consensus study was conducted, comprising six stages: 1) A systematic search of peer-reviewed and grey literature; 2) A series of roundtables with key stakeholders including social media companies, policymakers, and young people; 3) Questionnaire development; 4) Expert panel formation; 5) Data collection and analysis; and 6) Guideline development. Results A total of 191 items were included in the new #chatsafe guidelines. These were organised into eight themes, which became the overarching sections of the guidelines: 1) General tips; 2) Creating self-harm and suicide content; 3) Consuming self-harm and suicide content; 4) Livestreams of self-harm and suicide acts; 4) Self-harm and suicide games, pacts, and hoaxes; 6) Self-harm and suicide communities; 7) Bereavement and communicating about someone who has died by suicide; and 8) Guidance for influencers. Discussion The new guidelines include updated and new information on online communication about self-harm, livestreams, games, pacts, and hoaxes, as well as guidance for influencers. They will be disseminated via a national social media campaign and supported by a series of adult-facing resources. Given the acceptability of the original guidelines and the ubiquitous use of social media by young people, it is hoped that the new guidelines will be a useful resource for young people and adults alike, both in Australia and worldwide.