In 1908 she joined the Irish Women's Franchise League, created by her friend and fellow feminist Hanna Sheehy-Skeffington.

Around the same time she joined Cumann na mBan and from inside the organisation was critical of its restrained stance towards Redmond.

During this period Jacob also stood critical of the Third Home Rule Bill, as the grounds it contained nothing towards the suffrage of women.

During the 1918 Irish general election she canvassed on behalf of Éamon de Valera, but upon the meeting of the First Dáil was disappointed in its lack of female representation.

[4] Jacob opposed the Anglo-Irish Treaty of 1921 and supported cause the Anti-Treaty IRA in the Irish Civil War, however, she sought peace above all, as did many in the labour movement.

She and her colleague Lucy Kingston were the two Irish delegates to the Third International Women's Congress for Peace and Freedom in Vienna in 1921.

It was also in 1926 that she followed De Valera and Countess Markievicz and their supporters out of Sinn Féin and into the Fianna Fáil party following a split over the policy of using Abstentionism against Dáil Éireann.

In 1927 Jacob resigned as secretary of the Irish branch of the WILPF but went on to attend the organisation's congress in Prague in 1929 accompanied by Hanna Sheehy-Skeffington.

[9] She played a leading role in the political campaign to secure Ryan's freedom from Nationalist Spain, and later worked to defend his reputation after news of his death in Nazi Germany became known.