The boycott across Facebook, Instagram and Twitter channels runs from 3pm on Friday through until 11.59pm on Monday night.
William, who is president of the Football Association, announced on Twitter that he is joining the action.
Signing off the tweet with his first initial, he said: "As President of the FA I join the entire football community in the social media boycott this weekend. W"
Athletes, broadcasters and sponsors are involved in the plans too - which comes amid a rising tide of racist and sexist abuse directed on various social media platforms.
Many are calling on the platforms to do more to stamp out abuse, with harsher punishments for those found guilty.
Thierry Henry has called football’s social media boycott this weekend a “start” in the fight against racism and discrimination.
Last month, the now-retired Arsenal great removed himself from social media because of racism and bullying across the platforms.
Henry told CNN Sport: "It's not a safe place and it's not a safe environment.
"I wanted to take a stand on saying that it is an important tool that unfortunately some people turn into a weapon because they can hide behind a fake account."
“(What) the world of English football is doing at the minute and what’s going to happen at the weekend, people ask me, ‘Is it enough, the weekend?’," he told CNN.
“And I’m like, ‘It’s a start’. You know, you can’t be too greedy from not having anything to that. It’s a start."
Here is a look at some of those involved.
The sport’s authorities kicked off the boycott plans last Saturday night, in response to a rising tide of online hate aimed at players, managers and pundits.
Clubs across the Premier League, EFL, Women’s Super League and Women’s Championship will switch off their accounts.
Governing bodies’ central accounts – such as those belonging to the Premier League, the Football Association, the WSL, the EFL, the Professional Footballers’ Association, the League Managers Association and the Football Supporters’ Association are also involved, as are anti-discrimination bodies Kick It Out and Show Racism The Red Card.
Clubs and governing bodies across Scottish football have also now pledged to support the boycott.
Championship clubs Swansea City and Birmingham City, along with Scottish champions Rangers have previously adopted a social media blackout earlier in the campaign following racist abuse aimed at players online.
On the pitch, Rangers midfielder Glen Kamara was racially abused by Slavia Prague defender Ondrej Kudela during their Europa League clash.
Rangers' Glen Kamara on why he's speaking out after racist abuse
Liverpool captain Jordan Henderson handed his social media accounts over to an anti-cyberbullying earlier this month.
Discrimination in the sport appears to be on the rise. In September, the start of the 2021-21 season, Kick It Out said there had been a 42% increase in reports of discrimination. Reports of racism in the professional game rose by 53%.
The England and Wales Cricket Board announced on Wednesday that it, the 18 first-class counties, the eight women’s regional teams and the Professional Cricketers’ Association were joining the boycott.
The Rugby Football Union stands in solidarity with the football and cricket authorities, and its accounts for England Rugby, the Allianz Premier 15s, the Championship and GB7s will all suspend activity, it was confirmed on Thursday.
Clubs in the Gallagher Premiership announced they were boycotting social media the previous day, with the support of the Rugby Players’ Association.
The Lawn Tennis Association announced on Monday its intention to stand with football in support of the boycott.
World champion Sir Lewis Hamilton says he will shut down his social media activity, as will Williams driver George Russell.
But, at the moment, there is no wider commitment from F1 at this weekend's Portuguese Grand Prix.
Sportswear giant Adidas – which manufactures more than a third of Premier League kits – is stopping all advertising across its platforms.
Barclays, which sponsors the WSL, will support the blackout, with no social media posts on the Barclays Football pages of Facebook and Instagram nor the Barclays Footy Twitter account, while the company’s other social channels will avoid all football-related activity.
England football team sponsor Budweiser has signed up, while online car retailer Cazoo – which sponsors Everton and Aston Villa – became the first major sponsor to announce its support of the boycott on Tuesday.
BT Sport says the only posts on its channels over the blackout period will relate to social media abuse while talkSPORT is also supporting the boycott. Sky Sports, a key supporter of Kick It Out, is also understood to be backing the campaign.
Ahead of the boycott, BT Sport said: "This horrific cycle of online abuse needs to end. We stand united with the football community against online hate."
It added: "The only content to appear on our channels across this weekend will be in relation to social media abuse."
Head of talkSPORT Lee Clayton said: "talkSPORT is proud to join the social media boycott to speak up for those who have suffered real and lasting abuse on social media.
"talkSPORT's social media is an important part of our multimedia offering with 5.6m followers across our social platforms. But now is the time to stand with the football community against hate.
"Racism is of course a big part of this boycott. But it also spans sexism, hateful and hostile content, discrimination and general abuse too.
"As a station we are taking steps to protect our own presenters from abuse from social media trolls and this is an important statement that online hate will not be tolerated."
Culture secretary Oliver Dowden suggested that racist abuse will be among the harms that social media companies have to stamp out.
Writing in newspapers, he said: “Under the legislation, if social media companies do not keep their promises to users by, for example, failing to remove racist abuse, they will face severe sanctions.
“We could see fines of up to ten per cent of annual global turnover. For a company such as Facebook or YouTube, that could be billions.”
He added that the threat of enforcement would get social media companies to act.