He made first-class appearances for a number of teams, including Middlesex as a wicket keeper and captained the county club between 1898 and 1907.

[1] In 1889 and 1890 he appeared as full back for Cambridge University against Oxford, showing himself a fine tackler and a very accurate kick.

Five Scots were selected for Middlesex: Gregor MacGregor, George Campbell, William Wotherspoon, Robert MacMillan and Frederick Goodhue, all with London Scottish who played in the county.

[8] MacGregor was selected by the Scottish Rugby Union to appear for Scotland in all three international matches of the 1890 Home Nations Championship.

Although he began and finished his career in matches as a full back, MacGregor played mostly in those games as a centre three-quarter—those when the three three-quarter system was preferred.

For example, he contributed a chapter titled "Full Back Play" to a book by Bertram Fletcher Robinson, Rugby Football (London: The Isthmian Library, 1896).

[9][10] A portrait painted by Henry Weigall Jr, of Andrew Stoddart batting and MacGregor keeping wicket, was given to the MCC in 1927 by W.H.