Scottish Labour MSPs, including Carol Mochan, are also attending picket lines outside stations to show solidarity with workers.
A number of Labour MPs also posted on social media from picket lines.
A Scottish Labour spokesperson said no guidance had been issued to MSPs to avoid picket lines on Tuesday.
The spokesman said there were no concerns over a lack of unity within the party as he said there was a “different tone to the debate in Scotland”.
Tweeting as he attended the strike, Mr Sarwar said: “Solidarity with those on the picket lines. This is a crisis entirely of the Government’s making.
"The workers don’t want strikes, the unions don’t want strikes, the public don’t want strikes. They demand better.”
ScotRail has cancelled 90 per cent of its services, while cross-border operators have also been badly affected after last-ditch talks between the Rail, Maritime and Transport (RMT) union and Network Rail failed on Monday.
Labour has accused the UK Government of a “catastrophic failure of leadership” over the strike.
The spokesman added: "Fundamentally, the Labour party across the UK is clear that this is the responsibility of Government ministers and they’ve failed.
“Workers don’t want to go on strike. They’ve pushed into a position where they don’t want to go on strike.
“We’re supporting workers who feel like they’ve been pushed into a corner by Grant Shapps and Tory ministers and we will continue to do so.”
A senior Labour MP has warned colleagues that joining picket lines in support of striking workers will not resolve the dispute on the railways.
Shadow Treasury chief secretary Pat McFadden said he understood why the RMT was pressing for a pay rise due to the rising cost of living, but that he wanted to see a negotiated settlement.
The Conservatives have sought to use the row to claim Labour is on the side of the striking workers, who have contributed to chaos for millions of commuters.
However, the SNP has said “no-one should be fooled” as Scottish Labour “are still happy to be a branch office of Keir Starmer’s labour party”.
A spokesperson said: “[Scottish Labour] are working hand in glove with the Tories in a bid to thwart democracy in Scotland."
The Scottish Liberal Democrats said the “real villains" were Tory ministers during a time Scots are "desperate" for a summer holiday.
Jill Reilly, the Lib Dems transport spokesperson, said: "It's strange to see Keir Starmer ordering Labour parliamentarians not to support workers standing up for a pay rise in the middle of a cost-of-living crisis.
"The real villains of the piece though are Conservative ministers who have chosen to grandstand for months, rather than getting their hands dirty and striking a deal.
"Grant Shapps should resign.”