As a Radical representing first, with Daniel O'Connell's endorsement, Dundalk (1835-1837) and then, with the support of Chartists, the English constituency of Rochdale (1841–1852) he introduced bills to codify and extend in Ireland the Ulster tenant right.

In his last electoral contest, standing on the platform of the all-Ireland Tenant Right League in 1852 he failed to unseat the Conservative and Orange party in Down, his native county.

When he stood as a Westminster candidate for parliamentary reform in Down in 1831 and in Belfast in 1832, he was successfully opposed by the local Ascendancy interest (the dominant Downshire, Londonderry, and Donegall families).

[4][5] Sharman Crawford had resisted approaches from Daniel O'Connell in 1831 to join in the campaign to repeal of the Act of Union and to restore an independent Irish parliament.

He declared that the dissolution of the legislative union would "undermine the connection between Great Britain and Ireland upon which the prosperity, happiness, and security of the country depended" (Northern Whig, 24 Jan. 1831).

[4] He was encouraged when, in April 1842, 67 MPs (Sir Charles Napier and Richard Cobden among them) followed him into the Aye Lobby on his motion for Commons' committee to consider the Charter's Six Points.

Together with proposals for a union with the Anti-Corn Law League, Fergus O'Connor (the Irish-born leader of the democratic movement) saw the potential replacement of People's Charter as a threat to his position, and Sharman Crawford's move effected a split.

[10] But Davis's colleague at The Nation, Charles Gavan Duffy, forced the issue in an open letter that challenged O'Connell to affirm Repeal as his object.

In its report on the Irish land system, the commission, composed entirely of landowners, rejected the Ulster Custom, even while recognising its benefits, as dangerous to the "just rights of property".

[4] In 1848 with James MacKnight, editor of the liberal Londonderry Standard, and with the support of a group of radical Presbyterian ministers, Sharman Crawford formed the Ulster Tenant Right Association.

Some 48 Irish MPs were returned pledged "to hold themselves perfectly independent of, and in opposition to, all governments" which did not make passing Sharman Crawford's tenant-right bill a cardinal point of its policy.

[26] In December 1852, finding themselves holding the balance of power in the House of Commons, the Independent Irish MPs voted to bring down the Conservative ministry of Lord Derby.

But in the process two of the CDA leaders, John Sadlier and William Keogh, broke their pledges of independent opposition and accepted positions in a new Whig-Peelite ministry of Lord Aberdeen.

But the bills, which failed in the Lords, little impressed the League as landlords would have been left free to pass on the costs of compensation through their still unrestricted freedom to raise rents.

Tenant-right agitation died down and, although still submitting his thoughts on rural poverty and evictions to the press, the ageing Sharman Crawford withdrew from the public life.

In 1874 a reformed and enlarged electorate in Down, voting for the first time by secret ballot, returned his eldest surviving son, James Sharman Crawford, as a tenant-right Liberal.