thelandleague

At wikipedia. The photo there is 1895, and a lot less hair.

The catalogue says: Taken during a lecture tour of the United States.

Per that wikipedia article: Shortly before his arrest, Davitt had persuaded his family to emigrate to the United States. In July 1878, Davitt made a trip to visit them and raise money through a lecture tour to bring his mother and youngest sister back to Ireland (his father had since died). Upon his arrival in New York, he was welcomed by the United States-based republican organisation Clan na Gael and its leader, John Devoy. In its first such venture of the kind, the Clan organised Davitt's lecture tour, which lasted until December.

So July-December 1878, after he was in prison but before the Land War.

Flickr is sometimes amazing! Lots of images of Michael Davitt, gradually growing balder and beardier ...
"About 1880" via Paul O'Farrell
1884 book via Internet Archive Book Images
In 1895 via State Library Victoria Collections
In 1904 via TG4

One of only two men who spoke out publicly against the Limerick Pogrom, together with John Redmond. A true gentleman

I see the Wikipedia photo of 1895 is sourced from the State Library of Victoria (Australia), like a similarly dressed one above. Likely from a photo session when Michael Davitt visited Australia in that year. Via Trove a glowing contemporary description of the man ...
...Davitt came, not as a prince by the accident of birth, and with no other claim to a princely title, but as a prince among men by virtue of the possession of some of the rarest gifts of .Nature, a splendid intellect, a manly presence, and a self-sacrificing zeal for the welfare of his fellow-men. ...
... The secret of the love which people bear to Michael Davitt is further shown in the magnetic presence of the man. With a commanding figure, and a keenly intellectual face, there is an irresistible attraction which commands attention, and which inspires confidence and respect. Possessing a finely - strung nervous temperament, and with a face beaming with kindness, he still gives the impression that he possesses a reserve force of scathing sarcasm and fierce invective with which he could smite his enemies if occasion demanded. His language is unmistakable— clear, outspoken, and honest, every word bearing the mint mark of earnest conviction. ...

See - trove.nla.gov.au/newspaper/article/124811042

The Capuchin Archives think this is Irish National Convention of the Land League, Dublin, 1881.

I see a related Facebook page suggesting the bearded gent at left is Michael Davitt.

April 29th, 1880, in the Concert Room of the Rotunda in Dublin

The note on the back says:

Group of delegates at Rotunda Gardens
N.I.L. or Land League?
in eylidas [can't make that out]

On the front it says:
Richard Sheiling Sheehy Snr.
(2nd row, old man standing)

And at right there is an arrow identifying a David Sheehy

Niall McAuley More than happy to accept September 1881 if the Capuchin Archives say so.

Per the DIB: Sheehy, David (1844–1932), parliamentarian and agrarian radical, was born 14 October 1844 in Broadford, Co. Limerick, second of three children of Richard Sheehy, mill owner, and Johanna Sheehy (née O'Shea)