Yulia Navalnaya, the widow of the opposition leader Aleksei A. Navalny, lined up with voters outside the Russian embassy in Berlin on Sunday, in one of her few public appearances since her husband’s death last month.

Ms. Navalnaya has vowed to carry on her husband’s work. Her presence at the embassy on Sunday to vote in Russia’s presidential election appeared to be following one of Mr. Navalny’s last political exhortations before he died: Endorsing another activist’s call for opponents of President Vladimir V. Putin to show up at the polls on Sunday at noon local time.

Ms. Navalnaya declined to comment to reporters while standing in the mile-long line, flanked by her husband’s longtime spokeswoman, Kira Yarmysh. But she hugged and took photographs with supporters who approached her, some of them in tears.

After about six hours of waiting, Ms. Navalnaya emerged from the Russian Embassy. She told reporters that she had written in “Navalny” on her ballot.

By 1 p.m., the line of voters stretched for nearly a mile through central Berlin, ending just past a sign marking the location of Hitler’s World War II bunker. Several people waiting to cast ballots said they planned to vote for anyone other than Mr. Putin — even though the alternatives were Kremlin-approved candidates — or to write in Mr. Navalny’s name.

Yulia Lozovskaya, 29, who moved to Germany from St. Petersburg after Mr. Putin’s invasion of Ukraine, was one of many who sought out Ms. Navalnaya after learning on social media that she was standing somewhere in the line.

“You feel you’re not alone,” Ms. Lozovskaya said, referring to the size of the crowd. “And that gives enormous strength.”