Twitter Inc. has struck a deal to livestream free weekly baseball and hockey games with Major League Baseball's technology arm, adding another key piece in an expanding strategy to remake social media as a place where fans watch live sports on the same screen where they talk about them.

The pact announced Monday lets the social-networking company stream MLB and National Hockey League contests once a week, and launch a nightly highlight show covering multiple sports, though Canadians will once again find their access choked by local restrictions.

Exclusive rights agreements with Canadian broadcasters, notably Rogers Communications Inc., mean NHL games and Blue Jays games won't be streamed in Canada, though out-of-market baseball games will be allowed.

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Twitter's partnership with MLB Advanced Media (MLBAM) greatly expands the social network's nascent experiment in bringing live, televised sports online.

The company known for its 140-character messaging already has agreements to livestream 10 Thursday night National Football League games in the coming season – also blocked from Canada due to a rights agreement. – and with the National Basketball Association to stream behind-the-scenes video and original shows, as well as with the Pac-12 college sports conference.

Slow user growth at Twitter has left the social network searching for ways to broaden its appeal and deepen existing users' engagement, for fear of being left behind by rivals such as Facebook Inc., which now pays users to broadcast on its live video platform, and Snapchat Inc., which recently surpassed Twitter in daily users. That means Twitter is fighting to maintain its status as a place where users gather to follow live events as they unfold.

"This shows the importance of the social conversation around these live events, and how in-the-moment conversation has almost become a destination, and now a portal," said Christopher Doyle, head of media for Twitter Canada.

Mr. Doyle cites Twitter's recent livestreams of some Wimbledon tennis matches, with tweets attached to add context, as an early example of the plan, though the company has made forays into politics, livestreaming Donald Trump's Republican National Convention speech last week. Viewers can watch the livestreams whether or not they are logged into Twitter in most countries worldwide, which is crucial for sports leagues hoping to expand their fan bases outside North America.

"For Twitter, it's a way to distinguish themselves and have something that Facebook doesn't have," said Tom Richardson, president of Convergence Sports & Media and a professor of sports management at Columbia University.

A spokesperson for Twitter Canada confirmed that NHL and Blue Jays streams won't be available in Canada, nor will The Rally, the nightly highlight show.

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"Canadian sports fans already have lots of ways to watch all this content," said Scott Moore, president of Sportsnet and NHL properties at Rogers, in an interview. Mr. Moore said he would "never say never" to partnering with a social network to livestream games, but added, "We in the broadcast and cable world pay large sums of money for rights fees, and so far we've not seen the partnership that would make sense for us to share those rights."

Even U.S. users will only be able to stream out-of-market games in an effort to protect local broadcast rights, similar to local blackouts employed on TV. But Twitter's efforts to expand free access to prized sports broadcasts online further loosens traditional TV's grip on the lucrative live sports market, which has been a bastion of stability for cable and satellite providers under threat from new online rivals such as Netflix Inc.

In recent months, league executives have been entertaining pitches from digital-first bidders at events such as last month's Allen & Co. conference in Sun Valley, Idaho. Late last month, Walt Disney Co. bought a one-third stake in MLBAM, valuing the business at $3.5-billion (U.S.).

Financial terms of the new partnership were not disclosed, but Twitter will make revenue by selling ads on the live baseball and hockey broadcasts, either through preroll inside the livestream or promoted tweets accompanying it.

"I've got to imagine that there's decent potential, but to a certain extent it's got to be a loss leader [for Twitter] in the effort to get more users," Mr. Richardson said. "The leagues, the rights-holders, are experimenting while their partners foot the bill for the experiment."