Shlomo was born in 1912 to Ozer and Fruma Posner in Kowal, Włocławek, Poland. At age two, he lost his father. Another brother was born at the same time, named Ozer after their father. When Shlomo was five, his mother married Mordechai Rubinstein, and they had two children: Fella and Kazik. The house was Zionist, and this was Shlomo’s education. He studied in the Mizrahi School and Hebrew Gymnasium. At eighteen, he joined Beitar and met Yaakov Meridor.
In 1934, he was trained by Beitar in preparation for aliyah, which he made illegally in 1935. He lived in Tel Aviv and worked as a painter.
He was active in Beitar and joined the IZL.
In 1938, he left with Yaakov Meridor and some colleagues for Poland, in order to attend a course offered by the Polish Army to IZL members. When he returned, he commanded a course for IZL members in Mishmar HaYarden.
In the meantime, his brother Ozer made aliyah and joined Kibbutz HaShomer HaTza’ir. The two brothers met. Shlomo did not tell his brother about his underground activities. Four days after they met, everyone who had taken the course was arrested, including Shlomo. They were tried and sentenced to imprisonment. Shlomo spent four years in Acre Prison. He finally revealed to his brother, who had joined the Brigade and came to visit him in person, that he was imprisoned under an assumed identity.
In prison, he met Yair and joined him. After he was released, he continued his activity in Lehi. He worked in the Asis factory, and he gave most of his salary to the underground. He filled very senior roles and was in daily close contact with the central committee.
He was involved in management and finances, and he was connected to figures outside the underground which could help it. He was in constant contact with Yaakov Meridor, acting IZL commander until Menachem Begin was appointed. He arranged the transfer of Yaakov (Yashke) Eliav to Tel Aviv in an ambulance (he pretended to be ill), after he had fled from prison in Jerusalem. When massive arrests were made, Shlomo was taken to be identified, but since he carried his true identification, not the fake identification he had used while in prison, they let him go.
After the State was established, he worked selling replacement parts for cars.
In 1962, he married Hannah, who had a twelve-year-old daughter, Esther. They did not have children together. Shlomo collected paintings as a hobby.
He passed away on 15/6/1981.