Ms Thewliss announced the news on Twitter on Saturday evening, saying she would be a “clear contrast” to “two men shouting at each other across the dispatch box”.
Ms Thewliss wrote: “I’ve been working for independence for over half my life. Scotland is closer to achieving that now now than ever before.
“The Westminster group needs a leader who can build on Ian Blackford’s achievements and demonstrate that independence, far from being abstract, is the alternative to Brexit, the cost-of-living crisis and Tory austerity.”
Ms Thewliss said she had “no intention” of running, but now there is a vacancy, she believes she could do the job well and she has a “duty” to step up.
She is currently the party’s treasury spokesperson.
Ms Thewliss hit out at Westminster culture saying she would be a “clear contrast” to Keir Starmer and Rishi Sunak “shouting at each other” across the dispatch box.
The news comes after Ian Blackford announced he would not be restarting as Westminster leader at the party’s AGM next week amid speculation of a coup by Aberdeen South MP Stephen Flynn.
Mr Flynn has not yet publicly announced his intention to join the race.
The SNP’s Westminster Deputy Leader Kirsten Oswald will also stand down, according to tweets sent by the East Renfrewshire MP on Friday evening.